BEGIN:VCALENDAR
VERSION:2.0
PRODID:researchseminars.org
CALSCALE:GREGORIAN
X-WR-CALNAME:researchseminars.org
BEGIN:VEVENT
SUMMARY:Johan Ulander (Chalmers University of Technology)
DTSTART:20230830T111500Z
DTEND:20230830T120000Z
DTSTAMP:20260404T094647Z
UID:cam/1
DESCRIPTION:Title: Boundary-preserving numerical schemes for stochastic (partial) differen
tial equations\nby Johan Ulander (Chalmers University of Technology) a
s part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk
we consider stochastic (partial) differential equations whose solutions r
emain in some (half-)bounded domain. This includes\, for example\, models
for heat flow whose solutions remain positive. In general\, classical nume
rical schemes do not have the property of remaining in such domain. In thi
s half-way seminar\, I present some novel ideas for developing and analysi
ng boundary-preserving numerical schemes for stochastic (partial) differen
tial equations. The presentation is based on joint works with Charles-Edou
ard Bréhier\, David Cohen\, and Lluís Quer-Sardanyons.\n
LOCATION:https://stable.researchseminars.org/talk/cam/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yoshio Komori (Kyushu Institute of Technology)
DTSTART:20230906T111500Z
DTEND:20230906T120000Z
DTSTAMP:20260404T094647Z
UID:cam/2
DESCRIPTION:Title: Split S-ROCK methods for high-dimensional stochastic differential equat
ions\nby Yoshio Komori (Kyushu Institute of Technology) as part of CAM
seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe propose explicit stoch
astic Runge--Kutta (RK) methods for high-dimensional It\\^{o} stochastic d
ifferential equations. By providing a linear error analysis and utilizing
a Strang splitting-type approach\, we construct them on the basis of ortho
gonal Runge--Kutta—Chebyshev methods of order 2. Our methods are of weak
order 2 and have high computational accuracy for relatively large time-st
ep size\, as well as good stability properties. In addition\, we take stoc
hastic exponential RK methods of weak order 2 as competitors. It is shown
that the proposed methods can be very effective on high-dimensional proble
ms whose drift term has eigenvalues lying near the negative real axis and
whose diffusion term does not have very large noise. This is a joint work
with Prof. Kevin Burrage.\n
LOCATION:https://stable.researchseminars.org/talk/cam/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sagy Ephrati (University of Twente)
DTSTART:20230920T111500Z
DTEND:20230920T120000Z
DTSTAMP:20260404T094647Z
UID:cam/3
DESCRIPTION:Title: Stochastic modeling for coarse computational geophysical fluid dynamics
\nby Sagy Ephrati (University of Twente) as part of CAM seminar\n\nLec
ture held in MV:L14.\n\nAbstract\nStochasticity has been employed systemat
ically in geophysical fluid dynamics (GFD) to model uncertainty. Additiona
lly\, fully resolving geophysical flows is computationally expensive due t
o the large range of scales of motion present in these flows. These comput
ational costs are efficiently mitigated by performing GFD simulations on c
oarse computational grids and modeling the effects of unresolved scales on
resolved scales. On such grids\, the uncertainty due to unresolved small-
scale motions has to be taken into account as well as the loss of accuracy
due to poorly resolved spatial derivatives. In this presentation\, we dis
cuss how data assimilation methods can be used to derive data-driven stoch
astic forcing for coarse computational GFD. We will show that a straightfo
rward algorithm\, based on several simplifying assumptions\, already leads
to qualitatively accurate outcomes at strongly reduced computational cost
s.\n
LOCATION:https://stable.researchseminars.org/talk/cam/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Akash Sharma (Chalmers University of Technology and University of
Gothenburg)
DTSTART:20230913T111500Z
DTEND:20230913T120000Z
DTSTAMP:20260404T094647Z
UID:cam/4
DESCRIPTION:Title: Random walks for approximating boundary value problems\nby Akash S
harma (Chalmers University of Technology and University of Gothenburg) as
part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe will presen
t numerical method to simulate reflected stochastic differential equations
. We generalize this algorithm to approximately solve linear Robin boundar
y value problems via their probabilistic representations. In next part of
the talk\, we will present numerical schemes to simulate confined Langevin
dynamics which results in approximate solution of specular boundary value
problems. We obtain rate of convergence of these algorithms and verify th
em with numerical experiments. This is a joint work with Prof. Benedict Le
imkuhler (University of Edinburgh) and Prof. Michael V. Tretyakov (Univers
ity of Nottingham).\n
LOCATION:https://stable.researchseminars.org/talk/cam/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ioanna Motschan-Armen (Chalmers University of Technology and Unive
rsity of Gothenburg)
DTSTART:20230927T111500Z
DTEND:20230927T120000Z
DTSTAMP:20260404T094647Z
UID:cam/5
DESCRIPTION:Title: Euler-Maruyama approximations of the stochastic heat equation on the sp
here\nby Ioanna Motschan-Armen (Chalmers University of Technology and
University of Gothenburg) as part of CAM seminar\n\nLecture held in MV:L14
.\n\nAbstract\nThe stochastic heat equation on the sphere driven by additi
ve isotropic Wiener\nnoise is approximated by a spectral method in space a
nd forward and backward Euler–\nMaruyama schemes in time. The spectral a
pproximation is based on a truncation of the series\nexpansion with respec
t to the spherical harmonic functions. Optimal strong convergence rates\nf
or a given regularity of the initial condition and driving noise are deriv
ed for the Euler–\nMaruyama methods. Besides strong convergence\, conver
gence of the expectation and second\nmoment is shown\, where the approxima
tion of the second moment converges with twice the\nstrong rate. Numerical
simulations confirm the theoretical results.\nThis is joint work with Ann
ika Lang.\n
LOCATION:https://stable.researchseminars.org/talk/cam/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mohammad Asadzadeh (Chalmers & University of Gothenburg)
DTSTART:20231011T111500Z
DTEND:20231011T120000Z
DTSTAMP:20260404T094647Z
UID:cam/6
DESCRIPTION:Title: On Nitsche approach for a finite element scheme for Maxwell equations\nby Mohammad Asadzadeh (Chalmers & University of Gothenburg) as part of
CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe show improved conv
ergence for a $h-p$\, streamline diffusion (SD)\, Nitsche's scheme for the
Vlasov-Maxwell (VM) system. The standard Galerkin for VM equations\, as 1
st order hyperbolic\, suffers from the draw-back of poor convergence. We h
ave improved this convergence rate using: \n\n(i) The SD method that adds
artificial diffusion to the system.\n\n(ii) The $h-p$ approach to gain ada
ptivity feature. \n\n(iii) Combined\, differentiated\, Maxwell equations t
o render the first order hyperbolic system to a second order hyperbolic eq
uation (not applicable to Vlasov part). \n\n(iv) Add of {\\sl symmetry} an
d {\\sl penalty} terms to reach final step of Nitsche's scheme.\n\nNumeric
al examples are justifying the theory.\n
LOCATION:https://stable.researchseminars.org/talk/cam/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBA
DTSTART:20231018T111500Z
DTEND:20231018T120000Z
DTSTAMP:20260404T094647Z
UID:cam/8
DESCRIPTION:by TBA as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Institutionsdag
DTSTART:20231025T111500Z
DTEND:20231025T120000Z
DTSTAMP:20260404T094647Z
UID:cam/9
DESCRIPTION:by Institutionsdag as part of CAM seminar\n\nLecture held in M
V:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBA
DTSTART:20231101T121500Z
DTEND:20231101T130000Z
DTSTAMP:20260404T094647Z
UID:cam/10
DESCRIPTION:by TBA as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Luigi Romano (Chalmers University of Technology)
DTSTART:20231108T121500Z
DTEND:20231108T130000Z
DTSTAMP:20260404T094647Z
UID:cam/11
DESCRIPTION:Title: Finite element modelling of linear rolling contact problems\nby Lu
igi Romano (Chalmers University of Technology) as part of CAM seminar\n\nL
ecture held in MV:L14.\n\nAbstract\nThis Master's thesis deals with the nu
merical approximation of linear hyperbolic problems appearing in rolling c
ontact mechanics. First\, the existence and uniqueness of strict solutions
to the considered equations\, which contain nonlocal and boundary terms\,
are analysed within the framework provided by the semigroup theory. Then\
, the space semi-discrete problem is formulated using the discontinuous Ga
lerkin finite element method (DGMs)\, by replacing the unbounded operator
appearing in the abstract formulation with a finite-dimensional one. Quasi
-optimal error convergence is obtained for the space semi-discrete scheme
by introducing upwind regularisation. Time discretisation is then achieved
by relying on explicit first and second-order Runge-Kutta algorithms (RK1
and RK2\, respectively)\, yielding quasi-optimal convergence in time owin
g to certain refined CFL conditions. In particular\, the considered RK2 sc
hemes cover the explicit midpoint method\, Heun's second-order method\, an
d Ralston's method.\n
LOCATION:https://stable.researchseminars.org/talk/cam/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Moritz Hauck (Chalmers and GU)
DTSTART:20231115T121500Z
DTEND:20231115T130000Z
DTSTAMP:20260404T094647Z
UID:cam/12
DESCRIPTION:Title: Guaranteed lower energy bounds for the Gross-Pitaevskii problem using
mixed finite elements\nby Moritz Hauck (Chalmers and GU) as part of CA
M seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk\, we presen
t a lowest order Raviart-Thomas finite element discretization that provide
s guaranteed lower bounds on the ground state energy of the nonlinear Gros
s-Pitaevskii problem. We emphasize that due to their conformity\, classica
l discretization methods such as the $\\mathcal P^1$ or $\\mathcal Q^1$ fi
nite element methods can only provide upper bounds on the ground state ene
rgy. Furthermore\, we establish an a priori error analysis for the Raviart
-Thomas discretization of the Gross-Pitaevskii problem. Optimal convergenc
e rates are shown for the primary and dual variables as well as for the ei
genvalue and energy approximations.\n
LOCATION:https://stable.researchseminars.org/talk/cam/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Johannes Borgqvist (University of Oxford\, Chalmers and GU)
DTSTART:20231122T121500Z
DTEND:20231122T130000Z
DTSTAMP:20260404T094647Z
UID:cam/13
DESCRIPTION:Title: Lie symmetries for constructing\, selecting and analysing mechanistic
models in mathematical biology\nby Johannes Borgqvist (University of O
xford\, Chalmers and GU) as part of CAM seminar\n\nLecture held in MV:L14.
\n\nAbstract\nGiven the abundance of experimental data\, two of the most f
undamental questions in mechanistic modelling of biological data concern m
odel construction and model selection. A common type of data is time serie
s data describing how some quantity\, e.g. population size or protein abun
dance\, changes over time. Given such a time series\, it is often possible
to construct numerous candidate mechanistic models consisting of ordinary
differential equations based on physical principles encoding distinct bio
logical hypotheses. Worse still\, numerous candidate models of the same ti
me series often describe the same data equally well\, and thus they cannot
be distinguished based on their fit to data. In these situations it is th
erefore difficult to select one candidate model and thereby infer a biolog
ical mechanism underlying the biological data. In this presentation\, we t
ackle the two fundamental problems of model construction and model selecti
on by means of Lie symmetries (or simply just symmetries) of ordinary diff
erential equations. These are\, simply put\, (one parameter pointwise) tra
nsformations known as $\\mathcal{C}^{\\infty}$ diffeomorphisms which map a
solution curve to another solution curve. Symmetries are commonly used in
mathematical physics and they are the basis for numerous Nobel prizes but
they are almost unheard of in mathematical biology.\n\nTo solve the class
ical model selection problem\, we have developed and implemented a methodo
logy for model selection based on symmetries. We implement this framework
on actual experimental data describing the age-related increase in cancer
risk. Importantly\, we infer experimentally validated hypotheses underlyin
g different cancer types using the symmetry based framework which the stan
dard methodology based on model fitting fails to do. \n\nThereafter\, we s
witch focus to model construction in the context of travelling wave models
of collective cell migration. These models consists of a single second or
der ODE describing how the population density $u(z)$ changes with respect
to a travelling wave variable $z=x-ct$ where the constant $c$ is referred
to as the wave speed. Moreover\, certain such models of reaction diffusion
type as well as other models with density dependent diffusion are known t
o have specific analytical solutions of a simple form for certain wave spe
eds. These analytical solutions have been obtained by means of ansätze ba
sed on series expansions\, and using these methods it is difficult to defi
ne the class of models which have simple analytical solutions. To tackle t
his problem\, we consider a set of symmetries referred to as a Lie Algebra
consisting of two symmetries that has been used to find analytical soluti
ons of a second order ODE encapsulating numerous oscillatory models such a
s the van der Pol oscillator. Based on differential invariants\, we derive
the most general class of models for which this Lie Algebra is manifest.
Thereafter\, we implement Lie's algorithm based on step-wise integration i
n order to demonstrate how first integrals and (if possible) analytical so
lutions of all ODEs in our class of models are obtained. Using this genera
l class of models\, we construct a sub-class of models characterised by th
e previously mentioned simple analytical solution. Lastly\, we demonstrate
how this sub-class encapsulates the previously known models with analytic
al solutions and we quantify the action of the symmetries in this Lie alge
bra on these analytical solutions. In total\, this work demonstrates how c
lasses of mechanistic models can be constructed based on mathematical prop
erties encoded by a Lie Algebra in contrast to the standard way of model c
onstruction based on physical assumptions that are hard to validate.\n
LOCATION:https://stable.researchseminars.org/talk/cam/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Michael Roop (Chalmers and GU)
DTSTART:20231129T121500Z
DTEND:20231129T130000Z
DTSTAMP:20260404T094647Z
UID:cam/14
DESCRIPTION:Title: Lie-Poisson methods for incompressible magnetohydrodynamics on the sph
ere\nby Michael Roop (Chalmers and GU) as part of CAM seminar\n\nLectu
re held in MV:L14.\n\nAbstract\nWe present a novel structure preserving nu
merical method for Lie-Poisson systems on the dual of semidirect product L
ie algebras. The method fully preserves the underlying geometry\, namely t
he Lie-Poisson structure and all the Casimirs\, and nearly preserves the H
amiltonian function. We illustrate the method on two models describing the
motion of magnetic fluids\, the equations of incompressible magnetohydrod
ynamics\, and the Alfvén wave turbulence equations. For the latter case\,
we reveal the formation of large scale quasi-periodic vortex blob dynamic
s.\n\nThis is a joint work with Klas Modin.\n
LOCATION:https://stable.researchseminars.org/talk/cam/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBA
DTSTART:20231206T121500Z
DTEND:20231206T130000Z
DTSTAMP:20260404T094647Z
UID:cam/15
DESCRIPTION:by TBA as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tommy Svensson and Anders Logg (Chalmers)
DTSTART:20231213T121500Z
DTEND:20231213T130000Z
DTSTAMP:20260404T094647Z
UID:cam/16
DESCRIPTION:Title: Sustainable Urban C-V2X with Intelligent Radio Environment Twinning\nby Tommy Svensson and Anders Logg (Chalmers) as part of CAM seminar\n\n
Lecture held in MV:L14.\n\nAbstract\nUbiquitous connectivity to power Info
rmation and communication technologies (ICTs) is crucial for the modern so
ciety. Besides\, ICT also has an important role for accelerating economic
processes that enable sustainability. As one part of ICT in smart and sust
ainable cities\, cellular vehicle to everything (C-V2X)-based automated dr
iving will be crucial for fully autonomous or remotely operated vehicles i
n urban environments. To this end\, different communication technologies h
ave been developed to improve the efficiency and reliability of the networ
k performance\, such as millimeter wave communications and reconfigurable
intelligent surface (RIS). However\, challenges remain especially in urban
areas where the performance is normally hard to be evaluated before deplo
yments. Fortunately\, digital twinning can embed artificial intelligence a
nd ICT to provide a digital replica of real-life environments. With specif
ic characteristics\, the replica is almost a cloned version of the origina
l system\, and is able to constantly update the properties with real-time
data from sensors. In this presentation\, we will present recent progress
in our AoA-ICT Seed Project on programmable\, and environmental-suitable c
ommunication paradigm for C-V2X in dense city environments empowered by di
gital twinning.\n
LOCATION:https://stable.researchseminars.org/talk/cam/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eric Lindström (Chalmers and GU)
DTSTART:20240226T121500Z
DTEND:20240226T130000Z
DTSTAMP:20260404T094647Z
UID:cam/17
DESCRIPTION:Title: Multidimensional Coefficent Inverse Problems for Maxwellian Systems in
Conductive Media with Applications in Medical Imaging\nby Eric Lindst
röm (Chalmers and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n
\nAbstract\nThe talk will present a new method for medical imaging in the
context of coefficient inverse problems (CIPs) in maxwellian systems. The
main aim is to find potential tumors in human breasts by reconstructing th
e value and shape of spatial functions describing the dielectric propertie
s of various tissue types. The algorithms used for the hybrid method will
be introduced\, together with some theoretical results which discuss the w
ell-posedness of the underlying problem\, as well as the convergence of th
e reconstructing method. We will also look at numerical results achieved b
y applying our method to anatomically realistic data.\n
LOCATION:https://stable.researchseminars.org/talk/cam/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Rupp (Lappeenranta-Lahti University of Technology)
DTSTART:20240219T121500Z
DTEND:20240219T130000Z
DTSTAMP:20260404T094647Z
UID:cam/18
DESCRIPTION:Title: Partial differential equations on hypergraphs and networks of surfaces
\nby Andreas Rupp (Lappeenranta-Lahti University of Technology) as par
t of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nAlbeit many physi
cal\, sociological\, engineering\, and economic processes have been descri
bed by partial differential equations posed on domains which cannot be des
cribed as subsets of linear spaces or smooth manifolds\, there is still a
lack of mathematical tools and general purpose software specifically addre
ssing the challenges arising from the discretization of these models.\n\nT
his presentation establishes a general approach to formulate partial diffe
rential equations (PDEs) on networks of (hyper)surfaces\, referred to as h
ypergraphs. Such PDEs consist of differential expressions with respect to
all hyperedges (surfaces) and compatibility conditions on the hypernodes (
joints\, intersections of surfaces). These compatibility conditions ensure
conservation properties (in case of continuity equations) or incorporate
other properties – motivated by physical or mathematical modeling. We il
luminate how to discretize such equations numerically using hybrid discont
inuous Galerkin (HDG) methods. These methods consist of local solvers (enc
oding the differential expressions on hyperedges) and a global compatibili
ty condition (related to our hypernode conditions). We complement the phys
ically motivated compatibility conditions by a derivation through a singul
ar limit analysis of thinning structures yielding the same results.\n
LOCATION:https://stable.researchseminars.org/talk/cam/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Brynjulf Owren (NTNU Trondheim)
DTSTART:20240212T121500Z
DTEND:20240212T130000Z
DTSTAMP:20260404T094647Z
UID:cam/19
DESCRIPTION:Title: Stability of numerical methods on Riemannian manifolds\nby Brynjul
f Owren (NTNU Trondheim) as part of CAM seminar\n\nLecture held in MV:L14.
\n\nAbstract\nStability of numerical integrators play a crucial role in ap
proximating the flow of differential equations. Issues related to converge
nce and step size limitations have been successfully resolved by studying
the stability properties of numerical schemes. Stability also plays a role
in the existence and uniqueness to the solution of the nonlinear algebrai
c equations that need to be solved in each time step for an implicit metho
d.\nHowever\, very little has up to now been known about stability propert
ies of numerical methods on manifolds\, such as Lie group integrators. An
interest in these questions has recently been sparked by the efforts in co
nstructing ODE based neural networks that are robust against adversarial a
ttacks. In this talk we shall discuss a new framework for B-stability on R
iemannian manifolds. A method is B-stable if the numerical method exhibits
a non-expansive behaviour in the Riemannian distance measure when applied
to problems which have non-expansive solutions.\nWe shall in particular s
ee how the sectional curvature of the manifold plays a role\, and show som
e surprising results regarding the non-uniqueness of geodesic implicit int
egrators for positively curved spaces.\n
LOCATION:https://stable.researchseminars.org/talk/cam/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrea Papini (Chalmers and GU)
DTSTART:20240304T121500Z
DTEND:20240304T130000Z
DTSTAMP:20260404T094647Z
UID:cam/20
DESCRIPTION:Title: Turbulence enhancement of coagulating processes\nby Andrea Papini
(Chalmers and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbs
tract\nWe present and investigate the collision-coalescence process of par
ticles in the presence of a fluid velocity field\, examining the relations
hip between flow properties and enhanced coagulation. Our research focuses
on two main aspects. Firstly\, we propose a novel modeling approach for t
urbulent fluid at small scales\, employing a Gaussian random field with no
n-trivial spatial covariance. Secondly\, we derive rigorous partial differ
ential equations (PDEs) and stochastic partial differential equations (SPD
Es) from this model\, capturing the physical characteristics of particles
suspended in the fluid. From an Eulerian perspective\, we analyze a kineti
c particle system subjected to environmental transport noise. Specifically
\, we rigorously study a modified version of Smoluchowski’s coagulation
equation\, which incorporates velocity dependence akin to the Boltzmann eq
uation. By utilizing techniques rooted in unbounded elliptic semigroup the
ory and weighted Sobolev space inequalities\, we establish the existence a
nd uniqueness of classical solutions for the case of a spatially homogeneo
us initial distribution. Moreover\, from a Lagrangian viewpoint\, we emplo
y this particle system to gain insights into the collision rate at a stead
y state for particles uniformly distributed within a medium. Considering a
particle-fluid model\, we perform two scaling limits. The first limit\, i
nvolving the number of particles\, yields a stochastic Smoluchowski-type s
ystem\, with the turbulent velocity field still governed by a noise stocha
stic process. The second scaling limit pertains to the parameters of the n
oise\, specifically targeting the direction associated with small-scale tu
rbulence. This limit leads to a deterministic equation with eddy dissipati
on in the velocity variable. We conduct numerical simulations of this equa
tion system and demonstrate the influence of turbulence on rain formation.
Our qualitative findings reveal a steady increase in coagulation efficien
cy with escalating turbulent kinetic energy of the fluid. Additionally\, w
e observe a power-law decay over time and in relation to the turbulence pa
rameter. Furthermore\, we recover fundamental laws governing the collision
rate and relative velocity of moving particles in the high Stokes number
regime.\n
LOCATION:https://stable.researchseminars.org/talk/cam/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Verena Schwarz (University of Klagenfurt)
DTSTART:20240318T121500Z
DTEND:20240318T130000Z
DTSTAMP:20260404T094647Z
UID:cam/21
DESCRIPTION:Title: Higher-order approximation and optimality for jump-diffusion SDEs with
discontinuous drift\nby Verena Schwarz (University of Klagenfurt) as
part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk w
e consider the approximation of jump-diffusion stochastic differential equ
ations with discontinuous drift\, possibly degenerate diffusion coefficien
t\, and Lipschitz continuous jump coefficient. We present a jump-adapted h
igher-order scheme\, the so-called transformation-based jump-adapted quasi
-Milstein scheme. For this scheme\, we provide a complete error analysis:
We prove convergence order $3/4$ in $L^p$ for $p\\in[1\,\\infty)$. Further
\, we provide lower error bounds for non-adaptive and jump-adapted approxi
mation schemes of order $3/4$ in $L^1$. This yields optimality of the tran
sformation-based jump-adapted quasi-Milstein scheme.\n\nThis is joint work
with Pawel Przybylowicz and Michaela Szölgyenyi.\n
LOCATION:https://stable.researchseminars.org/talk/cam/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stefano Di Giovacchino (University of L'Aquila)
DTSTART:20240408T111500Z
DTEND:20240408T120000Z
DTSTAMP:20260404T094647Z
UID:cam/22
DESCRIPTION:Title: Stochastic backward error analysis: application to Hamiltonian systems
and optimization algorithms\nby Stefano Di Giovacchino (University of
L'Aquila) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\n
Backward error analysis is a powerful tool in order to capture the long-te
rm behaviour of numerical integrators. In this talk\, we address our atten
tion on providing a backward error analysis (both in the strong and weak s
ense) for classes of numerical methods. From one hand\, the attention will
be devoted to symplectic methods and Poisson integrators for stochastic H
amiltonian and Poisson systems. Here\, we present strategies for deriving
stochastic modified equations for the aforementioned integrators and we st
udy them for obtaining long-term estimates on the Hamiltonian errors along
the numerical dynamics.\nFrom the other hand\, the weak backward error ap
proach will be developed towards stochastic optimization algorithms\, with
the aim of gaining insights of their behaviour.\nThis talk is based on jo
int researches with Raffaele D'Ambrosio (University of L'Aquila)\, Desmond
J. Higham and Konstantios C. Zygalakis (University of Edinburgh).\n
LOCATION:https://stable.researchseminars.org/talk/cam/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fanny Seizilles (University of Cambride)
DTSTART:20240415T111500Z
DTEND:20240415T120000Z
DTSTAMP:20260404T094647Z
UID:cam/23
DESCRIPTION:Title: The Bayesian approach to inverse Robin problems\nby Fanny Seizille
s (University of Cambride) as part of CAM seminar\n\nLecture held in MV:L1
4.\n\nAbstract\nWe investigate the Bayesian approach to certain elliptic b
oundary value problems of determining a Robin coefficient on a hidden part
of the boundary from Cauchy data on the observable part. Such a nonlinear
inverse problem arises naturally in the initialisation of large-scale ice
sheet models. In this talk we will specifically focus on the computationa
l routine to estimate posterior densities for the Robin coefficient.\n\n\n
The Bayesian approach is motivated for a prototypical Robin inverse proble
m by showing that the posterior mean converges in probability to the data-
generating ground truth as the number of observations increases. Related t
o the stability theory for inverse Robin problems\, a logarithmic converge
nce rate for Sobolev-regular Robin coefficients is established\, whereas f
or analytic coefficients an algebraic rate can be attained. Our numerical
results on synthetic data illustrate the convergence property in two obser
vation settings. (Joint work with Aksel Kaastrup Rasmussen\, Ieva Kazlausk
aite and Mark Girolami).\n
LOCATION:https://stable.researchseminars.org/talk/cam/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Zheng Zhao (Uppsala University)
DTSTART:20240205T121500Z
DTEND:20240205T130000Z
DTSTAMP:20260404T094647Z
UID:cam/24
DESCRIPTION:Title: Moment quadrature for stochastic filtering\nby Zheng Zhao (Uppsala
University) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract
\nStochastic filtering is an important estimation problem for time series.
In this talk\, we present a class of filters that represent the filtering
distributions by their moments. The key enablement is a quadrature method
that uses orthonormal polynomials spanned by the moments. We show that th
is moment-based filter is asymptotically exact in the order of moments\, a
nd that the filter is also computationally efficient and is in line with t
he state of the art.\n
LOCATION:https://stable.researchseminars.org/talk/cam/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Axel Ringh (Chalmers and GU)
DTSTART:20240506T111500Z
DTEND:20240506T120000Z
DTSTAMP:20260404T094647Z
UID:cam/25
DESCRIPTION:Title: Gain and phase type multipliers for structured feedback robustness
\nby Axel Ringh (Chalmers and GU) as part of CAM seminar\n\nLecture held i
n MV:L14.\n\nAbstract\nOne of the most fundamental problems in control the
ory is feedback stability analysis. That is\, the problem of determining i
f two systems interconnected via feedback will be stable. In the case of l
inear time-invariant systems\, under mild conditions the solvability of a
set of linear matrix inequalities (LMIs) is a both necessary and sufficien
t condition for stability. Nevertheless\, models of reality are always imp
erfect\, and in robust stability analysis one therefore instead consider t
he problem if a feedback interconnection between a nominal system and a se
t of uncertainties is stable for all uncertainties in the set. In this tal
k\, I will present new results on that robustness to certain forms of stru
ctured uncertainties is equivalent with the existence of certain forms of
structured solutions to the LMIs. The talk is aimed to be self-contained\;
no prior knowledge on control theory is needed\, and all relevant concept
s will be introduced and explained.\n
LOCATION:https://stable.researchseminars.org/talk/cam/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Klas Modin (Chalmers and GU)
DTSTART:20240129T121500Z
DTEND:20240129T130000Z
DTSTAMP:20260404T094647Z
UID:cam/26
DESCRIPTION:Title: The reversibility paradox in matrix hydrodynamics\nby Klas Modin (
Chalmers and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbst
ract\nSome time ago\, Milo Viviani and myself unveiled numerical simulatio
ns of incompressible 2-D hydrodynamics on the sphere indicating a connecti
on between the long-time behavior of 2-D Euler equations and integrability
conditions for "blob dynamics". After presenting these results\, I was as
ked an insightful question:\n\nThe phase space underlying the model in the
simulations is compact. Because the dynamics in the model is also Hamilto
nian\, we have Poincaré recurrence. But the dynamics in the simulations\,
leading to blob formations\, seem contractive. Isn't the mechanism for bl
ob formations instead induced by fictitious dissipation\, introduced via t
he numerical time-discretization?\n\nI didn’t have a good answer at the
time\, but the question stayed with me. Today I have an answer\, which is
the subject of this talk.\n
LOCATION:https://stable.researchseminars.org/talk/cam/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eddie Wadbro (Karlstad University)
DTSTART:20240422T111500Z
DTEND:20240422T120000Z
DTSTAMP:20260404T094647Z
UID:cam/27
DESCRIPTION:Title: Material distribution topology optimization for boundary-effect-domina
ted problems\nby Eddie Wadbro (Karlstad University) as part of CAM sem
inar\n\nLecture held in MV:L14.\n\nAbstract\nIn the classical design optim
ization using the material distribution method (density-based topology opt
imization)\, a material indicator function represents the presence or abse
nce of material within the domain. The first part of this talk provides an
introduction to material distribution topology optimization with an empha
sis on mathematical morphology\, non-linear filters\, and length scale con
trol.\n\nTo use the material distribution approach for boundary-effect-dom
inated problems\, we need to identify the boundary of the design at each i
teration\; this talk discusses two methods to achieve this. The first is t
o use a boundary strip indicator function defined on the elements of the c
omputational mesh. The second is to use a boundary indicator function defi
ned on the mesh faces (edges in 2D and facets in 3D). The second part of m
y presentation covers the main ideas behind both approaches and showcases
results from two applications\, one suitable for each approach.\n
LOCATION:https://stable.researchseminars.org/talk/cam/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ragnar Winther
DTSTART:20240429T111500Z
DTEND:20240429T120000Z
DTSTAMP:20260404T094647Z
UID:cam/28
DESCRIPTION:Title: What about $p$?\nby Ragnar Winther as part of CAM seminar\n\nLectu
re held in MV:L14.\n\nAbstract\nThe title of this talk refers to a questio
n frequently asked by Ivo Babuska\, from the late 1980s and on\, following
various talks \non finite element methods. More precisely\, what can we s
ay about the properties of finite element methods as we raise the polynomi
al degree? Even today the so called $p$-method is less understood\,\nand t
he corresponding analysis is less canonical\, than the traditional approac
h of mesh refinement\, i.e.\, the $h$-method.\nIn recent years Rick Falk a
nd I have developed a theory which represents a new tool to analyze finite
element methods of high polynomial degree\,\nwhich we refer to as the b
ubble transform. The key idea is to construct a decomposition into local b
ubbles which \nsimultaneously covers all possible polynomial degrees.\nThe
purpose of this talk is to give a review of this theory\, and to discuss
\npotential applications.\n
LOCATION:https://stable.researchseminars.org/talk/cam/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Easter Monday
DTSTART:20240401T111500Z
DTEND:20240401T120000Z
DTSTAMP:20260404T094647Z
UID:cam/29
DESCRIPTION:by Easter Monday as part of CAM seminar\n\nLecture held in MV:
L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBC
DTSTART:20240527T111500Z
DTEND:20240527T120000Z
DTSTAMP:20260404T094647Z
UID:cam/30
DESCRIPTION:by TBC as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBC
DTSTART:20240610T111500Z
DTEND:20240610T120000Z
DTSTAMP:20260404T094647Z
UID:cam/31
DESCRIPTION:by TBC as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christian Lubich (University of Tübingen)
DTSTART:20240409T111500Z
DTEND:20240409T120000Z
DTSTAMP:20260404T094647Z
UID:cam/32
DESCRIPTION:Title: Regularized dynamical nonlinear parametric approximation\nby Chris
tian Lubich (University of Tübingen) as part of CAM seminar\n\nLecture he
ld in MV:L14.\n\nAbstract\nThis talk is about the numerical approximation
of solutions to initial value problems of high-dimensional ordinary differ
ential equations or evolutionary partial differential equations such as th
e Schr\\"odinger equation by nonlinear parametrizations $u(t)=\\Phi(q(t))$
with time-dependent parameters $q(t)$\, which are to be determined in the
computation. Our motivation comes from approximations by multiple Gaussia
ns in quantum dynamics\, by tensor networks\, and by neural networks. In a
ll these cases\, the parametrization is typically irregular: the derivativ
e $\\Phi'(q)$ can have arbitrarily small singular values and may have vary
ing rank. The talk is about approximation results for a regularized approa
ch\, which can still be successfully applied in such irregular situations\
, even if it runs counter to the basic principle in numerical analysis to
avoid solving ill-posed subproblems when aiming for a stable algorithm.\nT
he talk is based on joint work with Jörg Nick\, Caroline Lasser and Micha
el Feischl.\n
LOCATION:https://stable.researchseminars.org/talk/cam/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Malin Rau (Universität Hamburg)
DTSTART:20240311T121500Z
DTEND:20240311T130000Z
DTSTAMP:20260404T094647Z
UID:cam/33
DESCRIPTION:Title: Asynchronous Opinion Dynamics in Social Networks\nby Malin Rau (Un
iversität Hamburg) as part of CAM seminar\n\nLecture held in MV:L14.\n\nA
bstract\nOpinion spreading in society decides the fate of elections\, the
success of products\, and the impact of political or social movements.\nA
prominent model to study opinion formation processes is due to Hegselmann
and Krause. It has the distinguishing feature that stable states do not ne
cessarily show consensus\, i.e.\, the population of agents might not agree
on the same opinion.\n\nWe focus on the social variant of the Hegselmann-
Krause model. There are $n$ agents\, which are connected by a social netwo
rk. Their opinions evolve in an iterative\, asynchronous process in which
agents are activated one after another at random. When activated\, an agen
t adopts the average of the opinions of its neighbors having a similar opi
nion (where similarity of opinions is defined using a parameter $\\varepsi
lon$). Thus\, the set of influencing neighbors of an agent may change over
time. To the best of our knowledge\, social Hegselmann-Krause systems wit
h asynchronous opinion updates have only been studied with the complete gr
aph as social network.\n\nWe show that such opinion dynamics are guarantee
d to converge for any social network. We provide an upper bound of $\\math
cal{O}(n|E|^2 (\\varepsilon/\\delta)^2)$ on the expected number of opinion
updates until convergence to a stable state\, where $|E|$ is the number o
f edges of the social network\, and $\\delta$ is a parameter of the stabil
ity concept. For the complete social network\, we show a bound of $\\mathc
al{O}(n^3(n^2 + (\\varepsilon/\\delta)^2))$ that represents a major improv
ement over the previously best upper bound of $\\mathcal{O}(n^9 (\\varepsi
lon/\\delta)^2)$.\n
LOCATION:https://stable.researchseminars.org/talk/cam/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ioanna Motschan-Armen (Chalmers & GU)
DTSTART:20240617T091500Z
DTEND:20240617T100000Z
DTSTAMP:20260404T094647Z
UID:cam/34
DESCRIPTION:Title: Approximation of semilinear stochastic heat equations on the sphere\nby Ioanna Motschan-Armen (Chalmers & GU) as part of CAM seminar\n\nLect
ure held in MV:H12.\n\nAbstract\nStochastic partial differential equations
are used to describe various physical processes that are perturbed by noi
se. Some of those occur on curved surfaces\, for example spheres. In this
talk semilinear stochastic heat equations with additive noise on the unit
sphere are considered. Approximations in space and time are presented in o
rder to simulate and analyse solutions. The space approximation is derived
using the spectral method\, with spherical harmonic functions. In order t
o obtain time discretization on an equidistant time grid the Euler--Maruya
ma scheme is applied. For the semilinear stochastic heat equations on the
sphere with additive isotropic Wiener noise\, strong convergence rates in
space and time are derived\, taking regularity of the initial condition an
d the driving noise into account. Furthermore convergence of the expectati
on and the second moment is analysed for the corresponding linear equation
. The theoretical results are confirmed by numerical simulations.\n\nMidte
rm-Seminar\n
LOCATION:https://stable.researchseminars.org/talk/cam/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Charles-Edouard Bréhier (Université de Pau et des Pays de l'Adou
r)
DTSTART:20241007T111500Z
DTEND:20241007T120000Z
DTSTAMP:20260404T094647Z
UID:cam/35
DESCRIPTION:Title: Asymptotic error analysis of stochastic optimization schemes\nby C
harles-Edouard Bréhier (Université de Pau et des Pays de l'Adour) as par
t of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nStochastic optimi
zation algorithms are nowadays widely used\, especially in the machine lea
rning community. In this talk\, we study a class of stochastic optimizatio
n schemes which are perturbations of gradient descent algorithms.\nWe perf
orm a rigorous analysis of the convergence\, with proofs of error bounds w
ith respect to the time-step size\, in the large time regime\, in the case
of strongly convex objective functions. The error bounds follow from an i
nterpretation of the schemes in terms of deterministic and stochastic modi
fied equations\, and using tools from weak error analysis of numerical met
hods for stochastic differential equations.\n
LOCATION:https://stable.researchseminars.org/talk/cam/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mykola Tkachuk (Karlstad University)
DTSTART:20240923T111500Z
DTEND:20240923T120000Z
DTSTAMP:20260404T094647Z
UID:cam/36
DESCRIPTION:Title: Variational approaches to the analysis of structural response of fiber
network microstructures\nby Mykola Tkachuk (Karlstad University) as p
art of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nTwo approaches
to static equilibrium of fiber network microstructures will be presented.\
nOrientation-based averaging of network microstructures with non-affine ki
nematics associates the ensemble of fibers at a given material point with
a unit sphere of initial orientations (called also microsphere or represen
tative orientation space). A special micro-macro relation between these mi
croscopic deformations and the macroscopic deformation gradient is derived
by the concept of maximal advance paths in the network. The averaged micr
oscopic free energy of the fibers is minimized subjected to this kinematic
constraint. The derived model can be applied to networks of flexible poly
mer chains (as found in elastomers)\, semiflexible or stiff filaments (ela
stin\, collagen and other biopolymers and soft tissues). The model has bee
n recently extended to composite networks consisting of two or more distin
guished components. \nSliding of inextensible fibers in discrete network m
icrostructure of nonwoven materials is defined as a nonsmooth convex optim
ization problem. The rate-independent sliding and the quasi-static equilib
rium loading of such network structure are constituted within the theory o
f standard dissipative systems. A minimum principle for incremental potent
ial is formulated with respect to the displacement-based variables as a se
cond-order cone programming (SOCP) problem. A pure complementary energy pr
inciple is derived as the dual formulation in terms of stress-like variabl
es. Both SOCP problems can be solved numerically by interior-point methods
.\n
LOCATION:https://stable.researchseminars.org/talk/cam/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Workshop STINT: Sweden-China
DTSTART:20241014T111500Z
DTEND:20241014T120000Z
DTSTAMP:20260404T094647Z
UID:cam/37
DESCRIPTION:by Workshop STINT: Sweden-China as part of CAM seminar\n\nLect
ure held in MV:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrii Dmytryshyn (Örebro University)
DTSTART:20240902T111500Z
DTEND:20240902T120000Z
DTSTAMP:20260404T094647Z
UID:cam/38
DESCRIPTION:Title: Eigenstructures of low-rank matrix polynomials\nby Andrii Dmytrysh
yn (Örebro University) as part of CAM seminar\n\nLecture held in MV:L14.\
n\nAbstract\nChallenging and intriguing mathematical problems involving ma
trix polynomials arise in various applications. These problems often revol
ve around the eigenstructures of the polynomials\, emphasizing the importa
nce of the eigenstructures. In this talk we consider the set of matrix pol
ynomials of bounded rank and degree and describe the eigenstructures that
these polynomials typically have\, so called generic eigenstructures. We a
lso find such generic eigenstructures for the sets of symmetric and skew-s
ymmetric matrix polynomials. Notably\, these symmetries have drastic effec
t on generic eigenstructures\, for example\, on whether we can anticipate
the appearance of eigenvalues in the eigenstructures or not. \nThis talk i
s primarily based on joint work with Froilán Dopico and Fernando De Téra
n.\n
LOCATION:https://stable.researchseminars.org/talk/cam/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alex (Oleksandr) Misiats (Virginia Commonwealth University)
DTSTART:20240819T111500Z
DTEND:20240819T120000Z
DTSTAMP:20260404T094647Z
UID:cam/39
DESCRIPTION:Title: Linear Elastic Models of Shape Memory Alloys: Variational Perspective<
/a>\nby Alex (Oleksandr) Misiats (Virginia Commonwealth University) as par
t of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk\, I
will describe a class of minimization problems arising in modelling shape
memory alloys. I will start with a shape memory material illustration\, f
ollowed by a simple one dimensional model of it. Its extensions in 2D and
3D will help us understand the energetic mechanism behind the formation of
twin patterns in physical experiments. By means of sharp upper and lower
bounds\, we show that certain experimentally observed structures provide o
ptimal energy scaling law. Despite the fact that the problem is highly non
convex due to the presence of phase constraints and the singular perturbat
ion\, in my talk\, I will describe a relaxation method which allows the us
e of the convex duality technique for the purpose of obtaining a sharp low
er bound. I will also describe the extension of the linear elastic models
of two twins to model multiscale patterns\, which appear in recent physica
l experiments and involve mixing of four twins.\n
LOCATION:https://stable.researchseminars.org/talk/cam/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gabriel Velho (CentraleSupélec)
DTSTART:20240826T111500Z
DTEND:20240826T120000Z
DTSTAMP:20260404T094647Z
UID:cam/40
DESCRIPTION:Title: Stabilization and Optimal Control of Interconnected SDE - Scalar PDE S
ystem\nby Gabriel Velho (CentraleSupélec) as part of CAM seminar\n\nL
ecture held in MV:L14.\n\nAbstract\nIn this talk\, I will present my work
on the optimal control and stabilization of a system composed of an interc
onnected Stochastic Differential Equation (SDE) and a Scalar Partial Diffe
rential Equation (PDE)\, with control applied at the boundary of the PDE.
Such systems can be found in practical scenarios\, such as in temperature
control of a building where heat must be transmitted from a distance.\nI w
ill begin with an introduction to boundary control of PDEs\, emphasizing t
he backstepping method—a powerful technique for designing boundary contr
ollers that stabilize PDEs. In particular\, we will see how backstepping c
an be employed to stabilize a system of coupled hetero-directional transpo
rt equations.\nNext\, we will examine the complete system where this PDE i
s connected with an SDE at the boundary. I will show how backstepping tran
sforms this problem into an equivalent control problem for an input-delaye
d SDE\, making it more tractable.\nFinally\, I will discuss the implicatio
ns of input delays in controlling SDEs with additive noise\, particularly
how these delays impact system performance and the strategies we can use t
o mitigate these effects.\n
LOCATION:https://stable.researchseminars.org/talk/cam/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Malin Rau (Chalmers & GU)
DTSTART:20240916T111500Z
DTEND:20240916T120000Z
DTSTAMP:20260404T094647Z
UID:cam/41
DESCRIPTION:Title: Scheduling with Many Shared Resources\nby Malin Rau (Chalmers & GU
) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nConsider
the many shared resources scheduling problem where jobs have to be schedul
ed on identical parallel machines with the goal of minimizing the makespan
.\nHowever\, each job needs exactly one additional shared resource in orde
r to be executed and hence prevents the execution of jobs that need the sa
me resource while being processed.\nPreviously\, an approximation ratio of
asymptotically 2 was the best known result for this problem.\nFurthermore
\, a 6/5-approximation for the case with only two machines was known as we
ll as a PTAS for the case with a constant number of machines.\nWe present
a simple and fast 5/3-approximation and a much more involved but still rea
sonable 1.5-approximation.\nFurthermore\, we provide a PTAS for the case w
ith only a constant number of machines\, which is arguably simpler and fas
ter than the previously known one\, as well as a PTAS with resource augmen
tation for the general case.\nThe approximation schemes make use of the N-
fold integer programming machinery\, which has found more and more applica
tions in the field of scheduling recently.\nIt is plausible that the latte
r results can be improved and extended to more general cases.\nLastly\, we
give an inapproximability result for the natural problem extension where
each job may need up to a constant number of different resources\, namely
3\, ruling out better than 5/4 approximations for that case.\n
LOCATION:https://stable.researchseminars.org/talk/cam/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arnout Franken (University of Twente)
DTSTART:20240930T111500Z
DTEND:20240930T120000Z
DTSTAMP:20260404T094647Z
UID:cam/42
DESCRIPTION:Title: Casimir-preserving numerical methods for global geophysical fluid dyna
mics\nby Arnout Franken (University of Twente) as part of CAM seminar\
n\nLecture held in MV:L14.\n\nAbstract\nIn this talk\, I will present the
development of novel structure-preserving numerical methods for simulating
global geophysical fluid dynamics. The methods are derived using a geomet
ric approach to the quasi-geostrophic (QG) equations on a sphere\, reveali
ng their Lie-Poisson structure. This leads to energy and enstrophy-conserv
ing numerical methods that also preserve higher-order invariants\, known a
s Casimirs. These methods enable long-time simulations and are applied to
study geostrophic turbulence and its properties\, zonal jet formation\, an
d critical latitudes in both single- and multi-layer models. I'll discuss
both the development of the numerical methods and findings from simulation
s\, including insights into the role of geostrophic balance and stratifica
tion in large-scale global fluid dynamics.\n
LOCATION:https://stable.researchseminars.org/talk/cam/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristian Debrabant (University of Southern Denmark)
DTSTART:20241209T121500Z
DTEND:20241209T130000Z
DTSTAMP:20260404T094647Z
UID:cam/43
DESCRIPTION:Title: Optimal stochastic Runge-Kutta methods for the weak integration of sto
chastic dynamics\nby Kristian Debrabant (University of Southern Denmar
k) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nThe diff
iculty of the creation of weak high order integrators for stochastic dynam
ics lies in the tedious calculations of order conditions. The original app
roaches focused on adapting strong approximations\, mainly replacing the i
terated stochastic integrals by random variables that have the same moment
s. The methods obtained this way are sub-optimal in their number of functi
on evaluations.\n\nIn this talk\, using a specific set of random Runge-Kut
ta coefficients\, we greatly reduce the number of order conditions for wea
k second order integration of stochastic dynamics. The approach is success
fully applied to the creation of a collection of new simple stochastic Run
ge-Kutta methods of weak order two with an optimal number of stages.\n\nTh
e contents of this talk are joint work with Anne Kværnø and Adrien Laure
nt.\n
LOCATION:https://stable.researchseminars.org/talk/cam/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Johan Karlsson (KTH)
DTSTART:20241125T121500Z
DTEND:20241125T130000Z
DTSTAMP:20260404T094647Z
UID:cam/44
DESCRIPTION:Title: Structured multi-marginal optimal transport: Applications\, theory\, a
nd computations\nby Johan Karlsson (KTH) as part of CAM seminar\n\nLec
ture held in MV:L14.\n\nAbstract\nThe optimal mass transport problem is a
classical problem in mathematics\, and dates back to 1781 and work by G. M
onge where he formulated an optimization problem for minimizing the cost o
f transporting soil for construction of forts and roads. Historically the
optimal mass transport problem has been widely used in economics in\, e.g.
\, planning and logistics\, and was at the heart of the 1975 Nobel Memoria
l Prize in Economic Sciences. In the last two decades there has been a rap
id development of theory and methods for optimal mass transport and the id
eas have attracted considerable attention in several economic and engineer
ing fields. These developments have led to a mature framework for optimal
mass transport with computationally efficient algorithms that can be used
to address many problems in applied mathematics.\n\n \n\nIn this talk\, I
will give an overview of the multi-marginal optimal mass transport framewo
rk and show how it can be applied to address and solve a range of problems
in control and estimation of multi-agent systems. This the optimal transp
ort framework allows for replacing the standard state space formalist\, wh
ere a state evolve over time\, to a setting where instead densities or mul
ti-agent systems evolve over time. In this setting we can formulate and so
lve a large set of problems\, e.g.\, with given dynamics of the underlying
agents and multiple classes of agents\, nonlocal interactions\, or includ
e constraints between different time points such as origin destination con
straints. We will also consider computational methods\, and motivated by S
inkhorn's method for the standard optimal transport problems\, it can be s
hown that dual coordinate ascent is a computationally efficient approach f
or this class of problems. \n\nIn this talk\, I will give an overview of t
he multi-marginal optimal mass transport framework and show how it can be
applied to address and solve a range of problems in control and estimation
of multi-agent systems. This the optimal transport framework allows for r
eplacing the standard state space formalist\, where a state evolve over ti
me\, to a setting where instead densities or multi-agent systems evolve ov
er time. In this setting we can formulate and solve a large set of problem
s\, e.g.\, with given dynamics of the underlying agents and multiple class
es of agents\, nonlocal interactions\, or include constraints between diff
erent time points such as origin destination constraints. We will also con
sider computational methods\, and motivated by Sinkhorn's method for the s
tandard optimal transport problems\, it can be shown that dual coordinate
ascent is a computationally efficient approach for this class of problems.
\n
LOCATION:https://stable.researchseminars.org/talk/cam/44/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gunilla Kreiss (Uppsala University)
DTSTART:20241104T121500Z
DTEND:20241104T130000Z
DTSTAMP:20260404T094647Z
UID:cam/45
DESCRIPTION:Title: Cut FEM meets Finite Differences\nby Gunilla Kreiss (Uppsala Unive
rsity) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nTher
e is a cut-FEM methodology with ghost penalty stabilization\, which can be
applied to hyperbolic conservation laws. This technique is useful when co
nsidering problems with complex geometric features. Explicit time-stepping
is preferable for hyperbolic problems\, but even the standard DG and CG m
etods suffer from increasingly severe time-step restrictions as the order
of the method increases. For high order finite difference methods the time
-step restriction is not at all as severe. In this talk we will explore po
ssibilities of applying the cut-FEM methodology to finite difference metho
ds. The goal is to formulate a finite difference method that can be seen a
s a Galerkin method. Applying the cut-FEM methodology will then yield an i
mmersed boundary finite difference metod.\n
LOCATION:https://stable.researchseminars.org/talk/cam/45/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Björn Müller (Chalmers & GU)
DTSTART:20241118T121500Z
DTEND:20241118T130000Z
DTSTAMP:20260404T094647Z
UID:cam/46
DESCRIPTION:Title: Isotropic Q-fractional Brownian motion on the sphere: regularity and f
ast simulation\nby Björn Müller (Chalmers & GU) as part of CAM semin
ar\n\nLecture held in MV:L14.\n\nAbstract\nAs an extension of isotropic Ga
ussian random fields and Q-Wiener processes on d-dimensional spheres\, iso
tropic Q-fractional Brownian motion is introduced and sample Hölder regul
arity in space-time is shown depending on the regularity of the spatial co
variance operator Q and the Hurst parameter H. The processes are approxima
ted by a spectral method in space for which strong and almost sure converg
ence are shown. The underlying sample paths of fractional Brownian motion
are simulated by circulant embedding or conditionalized random midpoint di
splacement. Temporal convergence and computational complexity are numerica
lly tested\, the latter matching the complexity of simulating a Q-Wiener p
rocess if allowing for a temporal error.\n
LOCATION:https://stable.researchseminars.org/talk/cam/46/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mika Persson (Chalmers & GU)
DTSTART:20241202T121500Z
DTEND:20241202T130000Z
DTSTAMP:20260404T094647Z
UID:cam/47
DESCRIPTION:Title: Decentralized control of teams of drones: A mixed collaborative/compet
itive game\nby Mika Persson (Chalmers & GU) as part of CAM seminar\n\n
Lecture held in MV:L14.\n\nAbstract\nSmall and inexpensive drones are incr
easingly used in surveillance\, reconnaissance\, and attack operations. Fu
ture drones are expected to operate autonomously in large swarms\, posing
challenges for traditional Surface-Based Air Defense (SBAD) systems\, whic
h rely on radar sensors and effectors like missiles or jamming. Swarms can
overwhelm SBAD systems due to their sheer numbers and economic asymmetry\
, as drones are significantly cheaper than defense systems. A potential co
untermeasure is deploying defensive swarms of small drones with sensors an
d effectors\, necessitating optimized swarm behavior and capability evalua
tion. The proposed project focuses on decentralized control of such swarms
using game theory\, addressing challenges in operational goal representat
ion\, situational awareness through sensing and communication\, and managi
ng uncertainty about enemy capabilities. These challenges are modeled by P
artially Observable Stochastic Games. Approximation techniques like Multi-
Agent Reinforcement Learning are explored\, leveraging algorithms like MAD
DPG and MAAC for mixed competitive and collaborative swarm-versus-swarm sc
enarios. While related works address components of the problem\, they fall
short of addressing the full complexity\, particularly in handling unknow
n drone numbers\, controlled sensing\, communication\, and intelligent adv
ersaries in a competitive game-theoretic framework.\n
LOCATION:https://stable.researchseminars.org/talk/cam/47/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Lucia Swoboda (Chalmers & GU)
DTSTART:20241111T121500Z
DTEND:20241111T130000Z
DTSTAMP:20260404T094647Z
UID:cam/48
DESCRIPTION:Title: On a Galerkin-Bubnov variational formulation for the heat equation in
anisotropic Sobolev spaces\, using the modified Hilbert transform\nby
Lucia Swoboda (Chalmers & GU) as part of CAM seminar\n\nLecture held in MV
:L14.\n\nAbstract\nThe modified Hilbert transform arises naturally when co
nsidering a Galerkin-Bubnov variational formulation for the heat equation
in anisotropic Sobolev spaces. In this talk\, I will introduce the modifie
d Hilbert transform and its main properties. I will explain how this opera
tor leads to unique solvability of a variational formulation in anisotropi
c Sobolev spaces and to stability in the case of space-time tensor product
discretization. Although the discrete inf-sup constant depending on the f
inite element mesh parameter initially suggests a reduced order of converg
ence due to the structure of Céa's lemma\, optimal convergence is observe
d for a large class of functions.\n
LOCATION:https://stable.researchseminars.org/talk/cam/48/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vincent Molin (Chalmers & GU)
DTSTART:20241028T121500Z
DTEND:20241028T130000Z
DTSTAMP:20260404T094647Z
UID:cam/49
DESCRIPTION:Title: From a greedy Bouncy Particle Sampler to transport accelerated simulat
ed annealing\nby Vincent Molin (Chalmers & GU) as part of CAM seminar\
n\nLecture held in MV:L14.\n\nAbstract\nIn this work we explore the connec
tion between sampling and optimization. Starting from the Bouncy Particle
Sampler\, we combine a continuous time simulated annealing formulation wit
h additional mode-seeking behaviour by biasing the exploration towards mod
es of the objective function. However\, trying to tune the new parameters
to achieve faster cooling leads us to intead consider a curve of probabili
ty measures. The second part of the talk is thus dedicated to considering
curve following in a space of probability measures. To conclude\, we demon
strate a particle algorithm inspired by this curve following idea.\n
LOCATION:https://stable.researchseminars.org/talk/cam/49/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Richard Pates (Lund University)
DTSTART:20241021T111500Z
DTEND:20241021T120000Z
DTSTAMP:20260404T094647Z
UID:cam/50
DESCRIPTION:Title: Optimal Control on Positive Cones\nby Richard Pates (Lund Universi
ty) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this
talk we will discuss a class of optimal control problems for dynamical sy
stems that preserve cones. Under a critical assumption on the cone\, the c
orresponding Bellman equation is satisfied by a linear function\, which ca
n be computed by convex optimization. Three special cases are derived as
examples. The first one\, where the positive cone is the set of positive s
emi-definite matrices\, reduces to standard linear quadratic control. The
second one\, where the positive cone is a polyhedron\, reduces to a recent
result on optimal control of positive systems. The third special case cor
responds to linear quadratic control with additional structure\, such as s
patial invariance\n
LOCATION:https://stable.researchseminars.org/talk/cam/50/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlos Jerez Hanckes (Universidad Adolfo Ibañez)
DTSTART:20241022T090000Z
DTEND:20241022T100000Z
DTSTAMP:20260404T094647Z
UID:cam/51
DESCRIPTION:Title: Cell Electropermeabilization Modeling Via Multiple Traces Formulation
and Time Semi-Implicit Multistep Coupling\nby Carlos Jerez Hanckes (Un
iversidad Adolfo Ibañez) as part of CAM seminar\n\nLecture held in MV:L14
.\n\nAbstract\nWe simulate the electrical response of multiple disjoint bi
ological 3D cells undergoing an electropermeabilization process. Instead o
f solving the boundary value problem in the unbounded volume\, we reduce i
t to a system of boundary integrals equations--the local Multiple Traces F
ormulation--coupled with nonlinear dynamics on the cell membranes. Though
in time the model is highly non-linear and poorly regular\, the smooth geo
metry allows for boundary unknowns to be spatially approximated by spheric
al harmonics. This leads to spectral convergence rates in space. In time\,
we use a multistep semi-implicit scheme. To ensure stability\, the time s
tep needs to be bounded by the smallest characteristic time of the system.
Numerical results are provided to validate our claims and future enhancem
ents are pointed out.\n
LOCATION:https://stable.researchseminars.org/talk/cam/51/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alex (Oleksandr) Misiats (Virginia Commonwealth University)
DTSTART:20241106T090000Z
DTEND:20241106T100000Z
DTSTAMP:20260404T094647Z
UID:cam/52
DESCRIPTION:Title: Regularity and asymptotic properties of nonlocal stochastic evolution
equations arising in chemical and biomedical models\nby Alex (Oleksan
dr) Misiats (Virginia Commonwealth University) as part of CAM seminar\n\nL
ecture held in MV:L15.\n\nAbstract\nThis talk is devoted to the influence
of stochastic perturbations on the long time behavior of nonlocal evolutio
n equations. I will start with a brief overview of the theory of stochasti
c evolution equations\, and their applications. I will specifically focus
on two of such models: the bidomain model of heart tissue\, and the aggre
gation-diffusion equation (Keller-Segel model).\n\nThe nonlocal character
of these equations can be present either in the differential operator (bid
omain) or in the reaction term (Keller-Segel). Using the fundamental conce
pts in the area of stochastic analysis\, semigroup theory and PDEs\, in my
talk\, I will address the effects of noise on the existence of global vs.
local solutions (Keller-Segel) and their regularity\, as well as the exis
tence of invariant measures (for the bidomain model)\, which is the key st
ep in establishing the qualitative behavior of the underlying physical sys
tem. \n\nThis is a joint project with Prof. Oleksandr Stanzhytskyi from Ky
iv National University\, Ukraine.\n\nLivestreaming not possible this time
due to unusual room.\n
LOCATION:https://stable.researchseminars.org/talk/cam/52/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Han Zhang (Shanghai Jiao Tong University)
DTSTART:20241122T121500Z
DTEND:20241122T130000Z
DTSTAMP:20260404T094647Z
UID:cam/53
DESCRIPTION:Title: Consistent inverse optimal control: methods and applications in roboti
cs\nby Han Zhang (Shanghai Jiao Tong University) as part of CAM semina
r\n\nLecture held in MV:L14.\n\nAbstract\nThe inverse linear-quadratic opt
imal control problem is a system identification problem whose aim is to re
cover the quadratic cost function and hence the closed-loop system matrice
s based on observations of optimal trajectories. The inverse optimal contr
ol framework not only offers a powerful framework to model and predict exp
ert behaviors.\n\nIn this talk\, I will introduce a couple of inverse opti
mal control formulations. Identifiability analysis for each formulation wo
uld be presented. With the persistent excitation assumptions\, we can furt
her show the presented algorithms are statistically consistent. In the end
\, inverse optimal control algorithms are applied in control algorithm des
ign for rehabilitation robot.\n
LOCATION:https://stable.researchseminars.org/talk/cam/53/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eugen Bronasco (University of Geneva)
DTSTART:20250127T121500Z
DTEND:20250127T130000Z
DTSTAMP:20260404T094647Z
UID:cam/54
DESCRIPTION:Title: Algebraic structures and a new order two method for sampling the invar
iant measure of Langevin dynamics\nby Eugen Bronasco (University of Ge
neva) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nThis
talk explores the problem of sampling the invariant measure of Langevin dy
namics through the lens of exotic aromatic forests — a specialized class
of graphs forming an algebra that represents the\nalgebra of differential
operators. Such algebraic structures play a fundamental role in particula
r for the numerical analysis of numerical integrators. We establish the co
nnection between exotic aromatic forests and numerical methods\, introduci
ng the relevant algebraic structures and their applications. A key focus i
s the construction of a novel method of order two for invariant measure sa
mpling\, derived using the framework of exotic aromatic forests. Additiona
lly\, we demonstrate how these tools\ngenerate order conditions with favor
able algebraic properties\, facilitate the representation of composition a
nd substitution in numerical integrators\, and support backward error anal
ysis and the\ncomputation of modified equations. We conclude with an overv
iew of a new Haskell package designed to automate computations involving g
raph algebras.\n\nPapers and preprints available at: www.unige.ch/~bronasc
o\n
LOCATION:https://stable.researchseminars.org/talk/cam/54/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probably no cam
DTSTART:20250407T111500Z
DTEND:20250407T120000Z
DTSTAMP:20260404T094647Z
UID:cam/55
DESCRIPTION:by Probably no cam as part of CAM seminar\n\nLecture held in M
V:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/55/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eastern
DTSTART:20250421T111500Z
DTEND:20250421T120000Z
DTSTAMP:20260404T094647Z
UID:cam/56
DESCRIPTION:by Eastern as part of CAM seminar\n\nLecture held in MV:L14.\n
Abstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/56/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probably no cam
DTSTART:20250623T111500Z
DTEND:20250623T120000Z
DTSTAMP:20260404T094647Z
UID:cam/57
DESCRIPTION:by Probably no cam as part of CAM seminar\n\nLecture held in M
V:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/57/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marie E. Rognes (Simula Research Laboratory)
DTSTART:20250210T121500Z
DTEND:20250210T130000Z
DTSTAMP:20260404T094647Z
UID:cam/58
DESCRIPTION:Title: Brain membranes and vasculature: a computational mathematics tale of d
imensional gaps\nby Marie E. Rognes (Simula Research Laboratory) as pa
rt of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nStructurally\, b
rain tissue is characterized by thin cell membranes and slender vessels\,
defining submanifolds of codimension one and two respectively. Functional
ly\, your brain fundamentally relies on the transport of ions and nutrient
s and movement of water in and between these spaces. These physiological p
rocesses are clearly crucial for brain function and health\, but the preci
se mechanisms and their association with neurodegenerative diseases such a
s Alzheimer's and Parkinson's disease and neurological events such as seiz
ures remain only partially understood. Notably\, mathematical and computat
ional modelling are beginning to play an important role in gaining new ins
ight. In this talk\, I will discuss key mathematical\, numerical and compu
tational challenges associated with modelling brain mechanics and transpor
t across scales with an emphasis on coupled systems of partial differentia
l equations with dimensional gaps.\n
LOCATION:https://stable.researchseminars.org/talk/cam/58/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Snorre Harald Christiansen (University of Oslo)
DTSTART:20250310T121500Z
DTEND:20250310T130000Z
DTSTAMP:20260404T094647Z
UID:cam/59
DESCRIPTION:Title: Mixed finite elements from the point of view of category theory\nb
y Snorre Harald Christiansen (University of Oslo) as part of CAM seminar\n
\nLecture held in MV:L14.\n\nAbstract\nI will first give an introduction t
o mixed finite elements by describing the main example (developed around 1
980 by Raviart\, Thomas and Nédélec but closely related to constructions
in differential topology by de Rham\, Weil and Whitney in the 1940ies). T
hen I will relate how many fundamental constructions in finite element the
ory can be described in terms of category theory. I will not assume prior
knowledge of the latter. I will argue that the concept of a sheaf provides
a unified framework for studying both continuous and discretized PDEs. Sh
eaf theory was first introduced by Leray in the 1940ies and later clarifie
d in the Cartan seminar in the 1950ies with in particular algebraic geomet
ry in mind. Applied sheaf theory is now a developing subject in many field
s.\n
LOCATION:https://stable.researchseminars.org/talk/cam/59/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Olof Runborg (KTH)
DTSTART:20250428T111500Z
DTEND:20250428T120000Z
DTSTAMP:20260404T094647Z
UID:cam/60
DESCRIPTION:Title: Solving Helmholtz Equation Using the Temporal Wave Equation\nby Ol
of Runborg (KTH) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbst
ract\nWe consider iterative methods for the Helmholtz equation that are ba
sed on the related time domain wave equation. In each iteration\, the solu
tion to the wave equation with a time-periodic forcing is computed and fil
tered in time. For Dirichlet and Neumann problems the iteration correspond
s to a linear and coercive operator which\, after discretization\, is reca
st as a positive definite linear system of equations that can be solved wi
th the conjugate gradient method. The main benefit of using these iteratio
ns comes when considering large scale problems. Implementing parallelized\
, high order methods that run efficiently on big computers is typically ea
sier to do for time domain methods than for traditional Helmholtz solvers.
We also show how the iterations can be used to turn a multiscale method f
or the wave equation into a multiscale method for the Helmholtz equation.\
n
LOCATION:https://stable.researchseminars.org/talk/cam/60/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Balázs Kovács (Paderborn University)
DTSTART:20250317T121500Z
DTEND:20250317T130000Z
DTSTAMP:20260404T094647Z
UID:cam/61
DESCRIPTION:Title: Numerical surgery for mean curvature flow of surfaces --- A numerical
analyst at the operating table\nby Balázs Kovács (Paderborn Universi
ty) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this
talk I would like to discuss some numerical algorithms for mean curvature
flow of two-dimensional surfaces through singularities.\nIt is well known
that geometric surfaces flows often undergo topological changes. For mean
curvature flow this has been heavily investigated by\, e.g.\, Hamilton\,
Huisken and Sinestrari\, and Brendle and Huisken.\nBased on these works we
will discuss an algorithm for mean curvature flow with numerical surgery\
, a process which automatically handles these topological changes\, by cut
ting away some surface-portions and closing the remaining parts by spheric
al caps.\nIn view of this\, the following ethical statement seems appropri
ate: None of the test subjects were permanently harmed during the experime
nts.\n
LOCATION:https://stable.researchseminars.org/talk/cam/61/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Larisa Beilina (Chalmers & GU)
DTSTART:20250203T121500Z
DTEND:20250203T130000Z
DTSTAMP:20260404T094647Z
UID:cam/62
DESCRIPTION:Title: Optimization approach for solution of parabolic inverse source problem
using partial boundary measurements\nby Larisa Beilina (Chalmers & GU
) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe will
present optimization approach for determination of the spatially distribut
ed source function in the parabolic PDE using partial boundary measurement
s.\n\nIn this talk we will:\n1) Present Lagrangian approach for solution o
f optimization problem and derive optimality conditions.\n\n2) Prove that
the regularized Tikhnov functional is Frechet differentiable and establish
the\nexistence and uniqueness of the solution for the inverse problem whe
n\nthe set of admissible data is bounded.\n\n3) Establish a local stabilit
y estimate for the unknown source term.\n\n4) Present numerical examples i
n 2D with noisy data.\n
LOCATION:https://stable.researchseminars.org/talk/cam/62/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kasper Bågmark (Chalmers & GU)
DTSTART:20250512T111500Z
DTEND:20250512T120000Z
DTSTAMP:20260404T094647Z
UID:cam/63
DESCRIPTION:Title: Revisiting nonlinear filtering through deep BSDE methods\nby Kaspe
r Bågmark (Chalmers & GU) as part of CAM seminar\n\nLecture held in MV:L1
4.\n\nAbstract\nIn this talk\, I present a new approach to the nonlinear f
iltering problem based on the deep Backward SDE (BSDE) method. We begin by
formulating a system of equations that captures the classical prediction
–update steps in Bayesian filtering. While the update step is tractable
up to a normalising constant\, the focus is on approximating the predictio
n step\, which involves evolving the prediction density over time. When th
e hidden state follows a Stochastic Differential Equation (SDE)\, the pred
iction density satisfies the Fokker—Planck equation\, a Partial Differen
tial Equation (PDE). We solve this PDE using a probabilistic BSDE represen
tation\, which we approximate through an optimisation scheme involving neu
ral networks\, stochastic gradient descent\, and the Euler—Maruyama meth
od. The approach is demonstrated on numerical examples\, and we numericall
y examine its strong convergence rate.\n
LOCATION:https://stable.researchseminars.org/talk/cam/63/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Johan Ulander (Chalmers & GU)
DTSTART:20250505T111500Z
DTEND:20250505T120000Z
DTSTAMP:20260404T094647Z
UID:cam/64
DESCRIPTION:Title: Boundary-Preserving Weak Approximations of some semilinear Stochastic
Partial Differential Equations\nby Johan Ulander (Chalmers & GU) as pa
rt of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe propose a bou
ndary-preserving numerical scheme for the weak approximations of some scal
ar-valued stochastic partial differential equations (SPDEs) that only take
s values in a bounded domain. We only impose regularity assumptions on the
drift and diffusion coefficients locally on the domain. In particular\, t
he drift and diffusion coefficients may be non-globally Lipschitz continuo
us and superlinearly growing outside the domain. The scheme consists of a
finite difference discretisation in space and a Lie--Trotter splitting fol
lowed by exact simulation and exact integration in time. The scheme conver
ges in the weak sense to the mild solution with rate 1/2 in space and 1/4
in time for globally Lipschitz continuous test functions. Numerical experi
ments confirm that the theoretical results are sharp and we compare the pr
oposed scheme to existing schemes for SPDEs.\n
LOCATION:https://stable.researchseminars.org/talk/cam/64/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Klas Modin (Chalmers & GU)
DTSTART:20250324T121500Z
DTEND:20250324T130000Z
DTSTAMP:20260404T094647Z
UID:cam/65
DESCRIPTION:Title: Emmy Noether’s theorem\nby Klas Modin (Chalmers & GU) as part of
CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nI wish to talk about
Noether’s theorem\, including its proof. The subject came up on the occa
tion of the newly published popular science book “Emmys teorem” by Jul
ia Ravanis.\n
LOCATION:https://stable.researchseminars.org/talk/cam/65/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jennifer Ryan (KTH)
DTSTART:20250224T121500Z
DTEND:20250224T130000Z
DTSTAMP:20260404T094647Z
UID:cam/66
DESCRIPTION:Title: Techniques for Data enhancement\nby Jennifer Ryan (KTH) as part of
CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nExtracting extra info
rmation from data can allow for more insight into the interaction between
disparate scales. It can also aid in minimising error and decreasing noise
in data. While the ability to move data from fine resolutions to coarser
resolutions is straight forward utilizing a multi-resolution analysis fra
mework\, moving data from a coarse resolution to a finer resolution while
reducing errors is more challenging. This relies on combining filtering t
echniques into the multi-resolution analysis framework. This approach has
the further advantage of requiring fewer computations to gain insight into
calculations such as for Bohm speed. In this talk\, we present methods f
or data enhancement through multi-resolution analysis and the Smoothness-I
ncreasing Accuracy-Conserving (SIAC) filtering framework. SIAC is known to
inherently take advantage of the underlying physics and allow for the ful
l resolution of the approximation and its derivatives in both the physical
domain and Fourier signal space. We discuss recent advances and reliance
of the approach on the underlying numerical method that generated the dat
a.\n
LOCATION:https://stable.researchseminars.org/talk/cam/66/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Simon Jacobsson (KU Leuven)
DTSTART:20250217T121500Z
DTEND:20250217T130000Z
DTSTAMP:20260404T094647Z
UID:cam/67
DESCRIPTION:Title: Approximating maps into Riemannian manifolds\nby Simon Jacobsson (
KU Leuven) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\n
Many interesting functions arising in applications map into Riemannian man
ifolds. We present an algorithm\, using the manifold exponential and logar
ithm\, for approximating such functions. Our approach extends approximatio
n techniques for functions into linear spaces in such a way that we can up
per bound the forward error in terms of a lower bound on the manifold's se
ctional curvature. Furthermore\, when the sectional curvature is nonnegati
ve\, such as for compact Lie groups\, the error is guaranteed to not be wo
rse than in the linear case.\n
LOCATION:https://stable.researchseminars.org/talk/cam/67/
END:VEVENT
BEGIN:VEVENT
SUMMARY:(cancelled) David Krantz (KTH)
DTSTART:20250519T111500Z
DTEND:20250519T120000Z
DTSTAMP:20260404T094647Z
UID:cam/68
DESCRIPTION:by (cancelled) David Krantz (KTH) as part of CAM seminar\n\nLe
cture held in MV:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/68/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexander Paul Lewis (Georg-August-University of Goettingen)
DTSTART:20250414T111500Z
DTEND:20250414T120000Z
DTSTAMP:20260404T094647Z
UID:cam/69
DESCRIPTION:Title: Fundamental theorem for mean square convergence of SDEs on Riemannian
manifolds\nby Alexander Paul Lewis (Georg-August-University of Goettin
gen) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn rec
ent years there has been a surge of interest in using stochastic different
ial equations on Riemannian manifolds for a wide range of purposes. For ex
ample in: molecular dynamics\, computer vision\, sampling and machine lear
ning. As such\, developing accurate algorithms has become critical to esti
mate solutions of manifold valued SDEs in both the weak and strong sense.
Moreover\, analysis of strong convergence gives us a deeper understanding
of the dynamics and evolution of SDEs\, which has yet to be studied in gre
at detail on manifolds.\n\nThe error rate for the Euler(-Murayama) method
on Riemannian manifolds in the weak sense has been established in [1] and
was found to be of global rate 1\; reflecting the classical result known E
uclidean space. However\, strong convergence rates of the Euler scheme hav
e yet to be derived. Though based on intuition\, it is not unreasonable to
expect that the manifold scheme has the same global rate as its Euclidean
counterpart of 1/2. \n\nBy following closely to the approach laid out in
the seminal works of Milstein\, we show how to generate high order strong
schemes on a Riemannian manifold with non-positive curvature. In particula
r\, we show that the Euler scheme has global rate 1/2\, and we present the
Milstein correction to the Euler scheme which yields a scheme of global o
rder 1. Finally\, we will formulate the manifold generalisation of the fun
damental theorem of strong convergence\, allowing us to obtain global conv
ergence rates for a wide range of numerical schemes. I will also present n
umerical experiments which illustrate the theoretical guarantees\, as well
as a counterintuitive example on 2-dimensional hyperbolic space. \n\nThe
talk will give an overview of results obtained in joint work with Karthik
Bharath and Michael Tretyakov.\n\n\n[1] Bharath\, K.\, Lewis\, A.\, Sharma
\, A. and Tretyakov\, M.V.\, 2023. Sampling and estimation on manifolds us
ing the Langevin diffusion. arXiv preprint arXiv:2312.14882.\n
LOCATION:https://stable.researchseminars.org/talk/cam/69/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Isabel Haasler (Uppsala University)
DTSTART:20250526T111500Z
DTEND:20250526T120000Z
DTSTAMP:20260404T094647Z
UID:cam/70
DESCRIPTION:Title: System identification in large populations using optimal transport
\nby Isabel Haasler (Uppsala University) as part of CAM seminar\n\nLecture
held in MV:L14.\n\nAbstract\nIdentifying the dynamics of individual agent
s from aggregate\, population-level data is a key challenge in many applic
ations\, ranging from biology to crowd dynamics and traffic systems. In re
cent years\, optimal transport theory has emerged as a powerful tool for m
odeling large populations of agents\, as it bridges a population-level vie
wpoint with an agent-level viewpoint.\n\nIn this talk\, I will show how op
timal transport can be used to identify agent dynamics from snapshot obser
vations of the full population. This idea extends even to heterogeneous po
pulations\, where the observed data results from a superposition of multip
le subpopulations\, each governed by distinct dynamics. In this case\, our
method simultaneously separates the population into ensembles and identif
ies each ensemble’s governing system\, using only aggregate snapshot obs
ervations.\n
LOCATION:https://stable.researchseminars.org/talk/cam/70/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Souad Mohaoui (Örebro University)
DTSTART:20250331T111500Z
DTEND:20250331T120000Z
DTSTAMP:20260404T094647Z
UID:cam/71
DESCRIPTION:Title: Tensor decomposition approaches for motion capture data completion.\nby Souad Mohaoui (Örebro University) as part of CAM seminar\n\nLecture
held in MV:L14.\n\nAbstract\nTensor decompositions are powerful tools for
analyzing high-dimensional data by breaking down multi-way arrays into sm
aller\, meaningful components. They help uncover patterns and handle missi
ng data effectively. In this work\, we consider two tensor decomposition m
ethods\, CANDECOMP/PARAFAC (CP) and Tucker\, to address the problem of gap
filling in motion capture (MoCap) data. The gap-filling problem in marker
-based MoCap systems occurs when markers become occluded or detached durin
g recording\, resulting in incomplete data. Tensor decompositions offer an
effective solution by leveraging the inherent multi-way structure of MoCa
p data. We develop and analyze different completion algorithms built upon
CP and Tucker decompositions\, and evaluate their performance across diffe
rent missing data scenarios. The algorithms are tested using motion captur
e sequences from the publicly available CMU and HDM05 datasets.\n
LOCATION:https://stable.researchseminars.org/talk/cam/71/
END:VEVENT
BEGIN:VEVENT
SUMMARY:CAM BBQ (tbc)
DTSTART:20250616T111500Z
DTEND:20250616T120000Z
DTSTAMP:20260404T094647Z
UID:cam/72
DESCRIPTION:by CAM BBQ (tbc) as part of CAM seminar\n\nLecture held in MV:
L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/72/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marc Boxberg (RWTH Aachen University)
DTSTART:20250825T111500Z
DTEND:20250825T120000Z
DTSTAMP:20260404T094647Z
UID:cam/73
DESCRIPTION:Title: Data-Driven Inversion for Ultrasonic Wave Propagation: From Full-Wavef
orm Inversion to Gaussian Process Emulation\nby Marc Boxberg (RWTH Aac
hen University) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstr
act\nFull-waveform inversion (FWI) is a powerful technique for reconstruct
ing subsurface properties from wavefield data\, typically employing adjoin
t-state methods to compute sensitivity kernels and optimize model paramete
rs. However\, in highly attenuative media\, strong energy dissipation comp
licates backpropagation\, posing challenges for gradient-based optimizatio
n methods.\nIn this talk\, I will discuss two alternative approaches to wa
vefield-based inversion\, using ultrasonic laboratory measurements as an e
xample application. First\, I will outline a standard FWI approach utilizi
ng conjugate-gradient optimization to iteratively refine P-wave velocity a
nd S-wave velocity. Second\, I will present a data-driven alternative: a G
aussian process emulator that approximates the misfit function over the pa
rameter space\, enabling efficient inversion without the need for explicit
backpropagation. This approach offers advantages in scenarios where tradi
tional FWI struggles due to high attenuation or limited data coverage. How
ever\, so far\, it has only been tested for determining P- and S-wave velo
cities as well as attenuation parameters in homogeneous rock samples. I wi
ll discuss potential extensions and applications beyond ultrasonic experim
ents\, highlighting broader implications for geophysical inversion problem
s.\n
LOCATION:https://stable.researchseminars.org/talk/cam/73/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Martin Hermann (moved to 24.09\,13:15-14:00) (University of Augsbu
rg)
DTSTART:20250922T111500Z
DTEND:20250922T120000Z
DTSTAMP:20260404T094647Z
UID:cam/74
DESCRIPTION:Title: Riemannian optimization methods for ground states of multicomponent Bo
se-Einstein condensates\nby Martin Hermann (moved to 24.09\,13:15-14:0
0) (University of Augsburg) as part of CAM seminar\n\nLecture held in MV:L
14.\n\nAbstract\nGround states of multicomponent Bose-Einstein condensates
can be described as minimizers of the Gross-Pitaevskii energy functional
on an infinite-dimensional manifold. For the computation of these minimize
rs\, we investigate a family of Riemannian optimization methods with respe
ct to different metrics. This allows a unified treatment of several algori
thms under a common framework and enables us to prove global and local con
vergence guarantees for important cases. Finally\, we also discuss extensi
ons to rotating condensates\, where uniqueness can no longer be guaranteed
.\n
LOCATION:https://stable.researchseminars.org/talk/cam/74/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probably no cam
DTSTART:20251013T111500Z
DTEND:20251013T120000Z
DTSTAMP:20260404T094647Z
UID:cam/75
DESCRIPTION:by Probably no cam as part of CAM seminar\n\nLecture held in M
V:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/75/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probably no cam
DTSTART:20251020T111500Z
DTEND:20251020T120000Z
DTSTAMP:20260404T094647Z
UID:cam/76
DESCRIPTION:by Probably no cam as part of CAM seminar\n\nLecture held in M
V:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/76/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nikos. I. Kavallaris (Karlstad University)
DTSTART:20250908T111500Z
DTEND:20250908T120000Z
DTSTAMP:20260404T094647Z
UID:cam/77
DESCRIPTION:Title: Network Dynamics via Topological Data Analysis and Equation-Free Metho
ds\nby Nikos. I. Kavallaris (Karlstad University) as part of CAM semin
ar\n\nLecture held in MV:L14.\n\nAbstract\nWe propose a computational fram
ework for analyzing the macroscopic dynamics of complex agent-based networ
ks by integrating Topological Data Analysis (TDA) with the Equation-Free M
ethod. The approach is demonstrated on Erdős–Rényi random networks. A
TDA-based filtration\, driven by the density of activated nodes\, yields a
coarse macroscopic observable defined via persistent Betti numbers\, enab
ling significant dimensionality reduction while preserving essential topol
ogy. Within the Equation-Free framework\, we construct a lifting procedure
based on topological features and identify a data-driven evolution law fo
r this variable. Finally\, we perform numerical bifurcation and stability
analyses to characterize the global behavior and qualitative transitions o
f the emergent dynamics. This is a joint work with Konstantinos Spiliotis\
, Ole Sönnerborn\, and Haralampos Hatzikirou\n
LOCATION:https://stable.researchseminars.org/talk/cam/77/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Håkon Andreas Hoel (University of Oslo)
DTSTART:20251208T121500Z
DTEND:20251208T130000Z
DTSTAMP:20260404T094647Z
UID:cam/78
DESCRIPTION:Title: Multi-index Monte Carlo method for semilinear stochastic partial diffe
rential equations\nby Håkon Andreas Hoel (University of Oslo) as part
of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe present an expo
nential-integrator based multi-index Monte Carlo method (MIMC) for weak ap
proximations of semilinear stochastic partial differential equations (SPDE
). We explore recent theoretical results on multi-index-coupled solutions
of SPDEs\, showing that such couplings are stable and satisfy multiplicati
ve error estimates\, and describe how this theory can be utilized to produ
ce a tractable Monte Carlo method for weak approximations. Numerical examp
les illustrating the performance of MIMC will also be included.\n
LOCATION:https://stable.researchseminars.org/talk/cam/78/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Elisabeth Larsson (Uppsala University)
DTSTART:20251103T121500Z
DTEND:20251103T130000Z
DTSTAMP:20260404T094647Z
UID:cam/79
DESCRIPTION:Title: Numerical modeling of the human diaphragm\nby Elisabeth Larsson (U
ppsala University) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAb
stract\nIn this talk\, we take a look at the challenges involved in modeli
ng the respiratory mechanics numerically. The focus is on the diaphragm\,
which is the main respiratory muscle\, and which is very thin with respect
to its size. Two main subproblems\, geometry reconstruction and solution
of elasticity PDEs in the geometry will be covered. We will discuss the ch
oice of an unfitted oversampled radial basis function partition of unity m
ethod\, and how it can help us in dealing with the thin geometry. We will
discuss what kind of analysis we can use for this type of method. Finally\
, numerical results will be shown for linearly elastic model problems in t
he diaphragm geometry.\n
LOCATION:https://stable.researchseminars.org/talk/cam/79/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gerhard Wanner (Université de Genève)
DTSTART:20251110T121500Z
DTEND:20251110T130000Z
DTSTAMP:20260404T094647Z
UID:cam/80
DESCRIPTION:Title: Landmarks in the History of Iterative Methods\nby Gerhard Wanner (
Université de Genève) as part of CAM seminar\n\nLecture held in MV:L14.\
n\nAbstract\nTalk by Gerhard Wanner\n\nJoint work with Martin J. Gander an
d Philippe Henry\n\nInnehåll\n\nI. Ancient Square Root Calculations (Baby
lon\, Egypt\, Heron\, Bakhshali manuscript).\n\nII. Fixed Point Iteratio
ns (Jamshid Ghiath ud-Din Al-Kashi\,\nNityananda\, Habash al-Hasib al-Mar
wazi\, J. Kepler\, J. Fourier).\n\nIII. Emergence of Newton's Method (I. N
ewton\, Chr. Wren\, J. Wallis and Newton on Kepler's Equation\, Th. Simpso
n).\n\nIV. Geometry of Newton's Method (J.~R. Mourraille\, A. Cayley\, G.
Julia\, J. Hubbard\, A. Douady).\n\nV. Error Estimates for Newton's Method
(J. Fourier\, A.-L. Cauchy\, L.V. Kantorovich).\n
LOCATION:https://stable.researchseminars.org/talk/cam/80/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Michael Roop (Chalmers & GU)
DTSTART:20251215T121500Z
DTEND:20251215T130000Z
DTSTAMP:20260404T094647Z
UID:cam/81
DESCRIPTION:Title: Structure preservation in geophysical fluid dynamics\nby Michael R
oop (Chalmers & GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nA
bstract\nGeophysical fluid dynamics (GFD) describes flows of fluids on a p
lanetary scale. We will discuss the recent contribution to the hierarchy o
f GFD models developed in [1]\, called thermal quasi-geostrophic (TQG) equ
ations on the sphere. We will give Arnold’s formulation of TQG. Surprisi
ngly\, the TQG equations are formulated in terms of Morrison-Greene bracke
ts (semidirect product brackets) discovered long ago for another theory -
magnetohydrodynamics (MHD). Further\, we will discuss the structure-preser
ving discretisation for TQG based on Zeitlin’s matrix equations and the
Lie-Poisson time integrator developed for semidirect products\, and finall
y we will see some simulations.\n\n[1] M. Roop\, S. Ephrati. Thermal quasi
-geostrophic model on the sphere: Derivation and structure-preserving simu
lation. Phys. Fluids. 37\, 096601. 2025.\n
LOCATION:https://stable.researchseminars.org/talk/cam/81/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Johan Wärnegård (Chalmers & GU)
DTSTART:20250929T111500Z
DTEND:20250929T120000Z
DTSTAMP:20260404T094647Z
UID:cam/82
DESCRIPTION:Title: Mathematical modeling of quantum fluids of light\nby Johan Wärneg
ård (Chalmers & GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\n
Abstract\nThis talk will revolve around the fascinating topic of quantum f
luid of lights and the mathematical modeling thereof. Quantum fluids of li
ght have attracted a lot of attention lately due to their ability to achie
ve strong nonlinear effects and to demonstrate macroscopic quantum phenome
na such as superfluidity. In contrast to ultra-cold gases exhibiting super
fluidity\, these quantum fluids of light constitute open quantum systems a
s they continually lose photons to the environment and thus need replenish
ment. This interplay of drive and loss with the fluid-like behavior gives
rise to rich and complex physical phenomena\, which in turn present both c
hallenges and opportunities to physicists and applied mathematicians alike
.\n
LOCATION:https://stable.researchseminars.org/talk/cam/82/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sagy Ephrati (Chalmers & GU)
DTSTART:20251027T121500Z
DTEND:20251027T130000Z
DTSTAMP:20260404T094647Z
UID:cam/83
DESCRIPTION:Title: Geometric regularisation of two-dimensional turbulence\nby Sagy Ep
hrati (Chalmers & GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\
nAbstract\nRegularisation of turbulent flows is essential for computationa
lly efficient forecasting. In this talk\, we highlight a geometric mechani
sm for regularising two-dimensional turbulence that preserves key conserve
d quantities. We begin with a high-level introduction to how energy is dis
tributed across scales in turbulent flows\, using energy spectra to quanti
fy turbulence intensity and to illustrate energy cascades that govern flow
evolution. We then discuss the conserved quantities unique to two-dimensi
onal turbulence and how they give rise to the inverse energy cascade. This
sets the stage for recent results on geometric regularisation\, which all
ows for control over the energy distribution to enable reduced-complexity
computations while retaining fundamental invariants and the inverse energy
cascade.\n
LOCATION:https://stable.researchseminars.org/talk/cam/83/
END:VEVENT
BEGIN:VEVENT
SUMMARY:CANCELLED Adam Andersson (Saab\, Chalmers & GU)
DTSTART:20251201T121500Z
DTEND:20251201T130000Z
DTSTAMP:20260404T094647Z
UID:cam/84
DESCRIPTION:by CANCELLED Adam Andersson (Saab\, Chalmers & GU) as part of
CAM seminar\n\nLecture held in MV:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/84/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Lucia Swoboda (Chalmers & GU)
DTSTART:20251124T121500Z
DTEND:20251124T130000Z
DTSTAMP:20260404T094647Z
UID:cam/85
DESCRIPTION:Title: Numerical simulation of beam network models\nby Lucia Swoboda (Cha
lmers & GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\
nNetwork models are used to describe complex structures in fiber-based mat
erials\, like paper\, and biological tissues\, such as blood vessels. In t
hese models\, fibers are represented as beams connected at nodes\, capturi
ng mechanical properties while reducing computational costs compared to fu
ll 3D simulations. This talk addresses two problems: (1) the elastic defor
mation of beam networks in a stationary setting\, and (2) the elastic wave
propagation in time-dependent simulations. Both problems\, derived from l
inear elasticity\, describe how materials respond to applied forces and mo
ments. I will present the key steps in the convergence analysis and error
estimates\, supported by numerical results. Finally\, I will introduce a t
wo-level overlapping domain decomposition method for efficient paralleliza
tion.\n
LOCATION:https://stable.researchseminars.org/talk/cam/85/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alfred Wärnsäter (KTH Royal Institute of Technology)
DTSTART:20251117T121500Z
DTEND:20251117T130000Z
DTSTAMP:20260404T094647Z
UID:cam/86
DESCRIPTION:Title: Multiple Target Tracking via Multimarginal Optimal Transport\nby A
lfred Wärnsäter (KTH Royal Institute of Technology) as part of CAM semin
ar\n\nLecture held in MV:L14.\n\nAbstract\nThe field of Multiple Target Tr
acking (MTT) deals with the task of estimating targets that appear\, disap
pear\, and move within a scene\, given data from noisy measurements. An im
portant step in an MTT algorithm is data association: determining if a det
ection is a false positive\, and if not\, which target it should correspon
d to. We find that this task is closely related to the field of multimargi
nal optimal transport (MMOT)\, which originally stems from the problem of
optimally moving dirt for the construction of roads. In this work\, we con
nect MTT with MMOT. Specifically\, we show how a popular evaluation metric
for MTT (the TGOSPA metric) can be cast as an MMOT problem\, allowing it
to be computed efficiently using techniques from the MMOT literature.\n
LOCATION:https://stable.researchseminars.org/talk/cam/86/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Start
DTSTART:20260119T121500Z
DTEND:20260119T130000Z
DTSTAMP:20260404T094647Z
UID:cam/87
DESCRIPTION:by Start as part of CAM seminar\n\nLecture held in MV:L14.\nAb
stract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/87/
END:VEVENT
BEGIN:VEVENT
SUMMARY:End
DTSTART:20260622T111500Z
DTEND:20260622T120000Z
DTSTAMP:20260404T094647Z
UID:cam/88
DESCRIPTION:by End as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/88/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mihály Kovács (Pázmány Péter Catholic University and Budapest
University of Technology and Economics and Chalmers University of Technol
ogy)
DTSTART:20260126T121500Z
DTEND:20260126T130000Z
DTSTAMP:20260404T094647Z
UID:cam/89
DESCRIPTION:Title: Neumann-Neumann type domain decomposition of elliptic problems on metr
ic graphs\nby Mihály Kovács (Pázmány Péter Catholic University an
d Budapest University of Technology and Economics and Chalmers University
of Technology) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstra
ct\nWe develop a Neumann-Neumann type domain decomposition method for elli
ptic problems on metric\ngraphs. We describe the iteration in the continuo
us and discrete setting and rewrite the latter as a preconditioner\nfor th
e Schur complement system. Then we formulate the discrete iteration as an
abstract\nadditive Schwarz iteration and prove that it converges to the fi
nite element solution with a rate that is\nindependent of the finite eleme
nt mesh size. We also show that the condition number of the Schur compleme
nt\nis bounded uniformly with respect to the finite element mesh size. We
discuss various numerical\nexamples of interest and compare the Neumann-Ne
umann method to other preconditioners.\n\nThis research was partially fund
ed by the Hungarian National Research\, Development and Innovation\nOffice
(NKFIH) through Grant no. K-145934.\n
LOCATION:https://stable.researchseminars.org/talk/cam/89/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ana Djurdjevac (University of Oxford)
DTSTART:20260202T121500Z
DTEND:20260202T130000Z
DTSTAMP:20260404T094647Z
UID:cam/90
DESCRIPTION:Title: Mean-field optimal control with stochastic leaders\nby Ana Djurdje
vac (University of Oxford) as part of CAM seminar\n\nLecture held in MV:L1
4.\n\nAbstract\nWe study optimal control problems for interacting agent sy
stems arysing in opinion dynamics\, where a large number of agents is infl
uenced by a fixed number of stochastic leaders. We consider a partial mean
-field limit\, leading to a McKean–Vlasov equation for the followers cou
pled to controlled stochastic dynamics for the leaders. We show that opti
mal controls for the finite-agent system converge to the optimal control o
f the limiting mean-field system\, providing a low-dimensional and computa
tionally efficient approximation of high-dimensional control problems. In
addition\, we propose efficient numerical methods for computing leader-bas
ed controls. We illustrate the theoretical results with numerical experime
nts for the Hegselmann–Krause opinion dynamics model. This is joint work
with N. Conrad\, C. Hartmann\, C. Schütte and S. Zimper.\n
LOCATION:https://stable.researchseminars.org/talk/cam/90/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jennifer K. Ryan (KTH)
DTSTART:20260209T121500Z
DTEND:20260209T130000Z
DTSTAMP:20260404T094647Z
UID:cam/91
DESCRIPTION:Title: Techniques for data enhancement\nby Jennifer K. Ryan (KTH) as part
of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nExtracting extra i
nformation from data can allow for more insight into the interaction betwe
en disparate scales. It can also aid in minimising error and decreasing no
ise in data. While the ability to move data from fine resolutions to coar
ser resolutions is straight forward utilizing a multi-resolution analysis
framework\, moving data from a coarse resolution to a finer resolution whi
le reducing errors is more challenging. This relies on combining filterin
g techniques into the multi-resolution analysis framework. This approach h
as the further advantage of requiring fewer computations to gain insight i
nto calculations such as for Bohm speed. In this talk\, we present method
s for data enhancement through multi-resolution analysis and the Smoothnes
s-Increasing Accuracy-Conserving (SIAC) filtering framework. SIAC is known
to inherently take advantage of the underlying physics and allow for the
full resolution of the approximation and its derivatives in both the physi
cal domain and Fourier signal space. We discuss recent advances and relia
nce of the approach on the underlying numerical method that generated the
data\n
LOCATION:https://stable.researchseminars.org/talk/cam/91/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christian Engström (Linnéuniversitetet)
DTSTART:20260309T121500Z
DTEND:20260309T130000Z
DTSTAMP:20260404T094647Z
UID:cam/92
DESCRIPTION:Title: Contour integral methods for time-fractional equations\nby Christi
an Engström (Linnéuniversitetet) as part of CAM seminar\n\nLecture held
in MV:L14.\n\nAbstract\nWe investigate a class of multiterm time-fractiona
l diffusion equations. The problem is reformulated as a perturbed paraboli
c Volterra equation\, which allows the use of Laplace transform techniques
and resolvent estimates. This approach is flexible and covers a wide rang
e of anomalous diffusion models with combined fractional and classical mem
ory effects. We also discuss implications for the design and analysis of h
igh-order accurate contour integral methods for such equations.\n
LOCATION:https://stable.researchseminars.org/talk/cam/92/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicola Guglielmi (Gran Sasso Science Institute)
DTSTART:20260330T111500Z
DTEND:20260330T120000Z
DTSTAMP:20260404T094647Z
UID:cam/93
DESCRIPTION:Title: The power of rank-1 perturbations in matrix nearness problems.\nby
Nicola Guglielmi (Gran Sasso Science Institute) as part of CAM seminar\n\
nLecture held in MV:L14.\n\nAbstract\nThis talk concerns matrix nearness p
roblems related to eigenvalues\, singular values\, and pseudospectra. Such
problems arise in a wide range of applications\, including dynamical syst
ems\, where they appear in questions of robust stability and control\, as
well as graph-based problems such as clustering and ranking. These problem
s lead to algorithms based on structured matrix perturbations that move ei
genvalues\, singular values\, or Rayleigh quotients to prescribed location
s.\n\nRemarkably\, the optimal perturbations are often of rank one\, or pr
ojections of rank-1 matrices onto a given linear structure\, such as a pre
scribed sparsity pattern. In the approach presented here\, these optimal r
ank-1 perturbations are computed by a two-level iteration combining eigenv
alue optimization with root-finding.\n\nThe eigenvalue optimization proble
m\, with equality or inequality constraints on the perturbation size\, is
solved using gradient-based differential equations for rank-1 matrices. In
practice\, this amounts to evolving two vectors that represent the rank-1
matrix toward a stationary point. The root-finding component determines t
he optimal perturbation size by solving a scalar nonlinear equation. The t
wo algorithmic components can either be nested or applied in an alternatin
g fashion. Numerical experiments illustrate the efficiency of the approach
for several eigenvalue- and singular-value–based nearness problems. \nT
he talk is largely based on a recent monograph written jointly with Christ
ian Lubich.\n
LOCATION:https://stable.researchseminars.org/talk/cam/93/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Michael Tretyakov (University of Nottingham)
DTSTART:20260413T111500Z
DTEND:20260413T120000Z
DTSTAMP:20260404T094647Z
UID:cam/94
DESCRIPTION:by Michael Tretyakov (University of Nottingham) as part of CAM
seminar\n\nLecture held in MV:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/94/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Lucia Swoboda (Chalmers and GU)
DTSTART:20260504T111500Z
DTEND:20260504T120000Z
DTSTAMP:20260404T094647Z
UID:cam/95
DESCRIPTION:by Lucia Swoboda (Chalmers and GU) as part of CAM seminar\n\nL
ecture held in MV:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/95/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrii Dmytryshyn (Chalmers and GU)
DTSTART:20260427T111500Z
DTEND:20260427T120000Z
DTSTAMP:20260404T094647Z
UID:cam/96
DESCRIPTION:by Andrii Dmytryshyn (Chalmers and GU) as part of CAM seminar\
n\nLecture held in MV:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/96/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Myklebust (Norwegian University of Life Sciences)
DTSTART:20260216T121500Z
DTEND:20260216T130000Z
DTSTAMP:20260404T094647Z
UID:cam/97
DESCRIPTION:Title: Finite element discretization of Yang–Mills connections\nby Andr
eas Myklebust (Norwegian University of Life Sciences) as part of CAM semin
ar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk I will present ong
oing work on finite element discretization of Yang–Mills connections on
principal bundles. To approximate Yang–Mills connections numerically\, w
e first choose local sections and partition the base manifold. This allows
us to represent connections as piecewise 1-forms with trace jumps across
interfaces prescribed by the sections. For bundles with abelian structure
group\, enforcing these jumps via Lagrange multipliers leads to a well-pos
ed saddle-point problem that can be solved using finite element methods. W
e illustrate the method on the Hopf bundle.\n
LOCATION:https://stable.researchseminars.org/talk/cam/97/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adam Andersson
DTSTART:20260525T111500Z
DTEND:20260525T120000Z
DTSTAMP:20260404T094647Z
UID:cam/98
DESCRIPTION:by Adam Andersson as part of CAM seminar\n\nLecture held in MV
:L14.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/98/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Easter
DTSTART:20260406T111500Z
DTEND:20260406T120000Z
DTSTAMP:20260404T094647Z
UID:cam/99
DESCRIPTION:by Easter as part of CAM seminar\n\nLecture held in MV:L14.\nA
bstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/cam/99/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Malin Mosquera (Chalmers and GU)
DTSTART:20260302T121500Z
DTEND:20260302T130000Z
DTSTAMP:20260404T094647Z
UID:cam/100
DESCRIPTION:Title: A Localised Orthogonal Decomposition Method for Heterogeneous Mixed-D
imensional Problems\nby Malin Mosquera (Chalmers and GU) as part of CA
M seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk\, we presen
t a model for solving mixed-dimensional elliptic problems with highly hete
rogeneous coefficients\, a type of problem that commonly appears in e.g. m
odelling of fractured porous media but can be computationally challenging
to solve numerically. Thin structures are modelled as lower-dimensional in
terfaces embedded in a higher-dimensional bulk domain\, leading to the mix
ed-dimensional model problem.\n\nOur method is based on the Localised Orth
ogonal Decomposition (LOD) method and constructs locally supported basis f
unctions on a coarse mesh that does not resolve the fine-scale variations
of the coefficients. The basis functions are adapted to the problem at han
d and thus carries the fine-scale information in order to ensure optimal c
onvergence with respect to the coarse mesh. This method leads to an expone
ntially decaying localisation error. We present numerical experiments to v
alidate the theoretical findings.\n
LOCATION:https://stable.researchseminars.org/talk/cam/100/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matthias Geilhufe (Chalmers)
DTSTART:20260323T121500Z
DTEND:20260323T130000Z
DTSTAMP:20260404T094647Z
UID:cam/101
DESCRIPTION:Title: Ultrafast Thermodynamics - towards entropy\, heat and criticality on
picosecond timescales\nby Matthias Geilhufe (Chalmers) as part of CAM
seminar\n\nLecture held in MV:L14.\n\nAbstract\nMaterials are composed of
a vast number of ions and electrons\, arranging themselves in regular patt
erns. Due to immense progress in ultrafast spectroscopy\, ranging from the
low-frequency infrared to high-frequency X-ray regimes\, collective excit
ations of charge\, spin\, lattice\, and orbital degrees of freedom can now
be triggered and probed on their characteristic time and length scales. P
robing such excitations far from equilibrium motivates the field of ultraf
ast thermodynamics\, which translates well-understood concepts\, such as e
ntropy and heat\, to picosecond dynamics. I will introduce the concept of
ultrafast thermodynamics using the example of entropy production due to la
ser-driven phonons [1] and magnons [2] using stochastic thermodynamics. I
will show that these processes are well described by Langevin equations an
d introduce their derivation on a few examples. Furthermore\, I will show
extensions of the formalism to non-Markovian behavior and quantum mechanic
s [3].\n\n\n[1] L. Caprini\, H. Löwen & R. M. Geilhufe\, Nature Communica
tions\, 15\, 94 (2024) \n\n[2] F. Tietjen\, R. M. Geilhufe\, PNAS Nexus\,
4\, 3 (2025)\n\n[3] Y. Qiao\, R. M. Geilhufe\, arXiv:2512.17669\n
LOCATION:https://stable.researchseminars.org/talk/cam/101/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arnulf Jentzen (School of Data Science & School of Artificial Inte
lligence\, The Chinese University of Hong Kong\, Shenzhen and Institute fo
r Analysis and Numerics\, University of Münster)
DTSTART:20260518T111500Z
DTEND:20260518T120000Z
DTSTAMP:20260404T094647Z
UID:cam/102
DESCRIPTION:Title: Comprehensive convergence analysis for the Adam optimizer\nby Arn
ulf Jentzen (School of Data Science & School of Artificial Intelligence\,
The Chinese University of Hong Kong\, Shenzhen and Institute for Analysis
and Numerics\, University of Münster) as part of CAM seminar\n\nLecture h
eld in MV:L14.\n\nAbstract\nIn the training of artificial intelligence (AI
) systems\, often not the standard gradient descent (GD) method is the emp
loyed optimization scheme but instead suitable accelerated and/or adaptive
GD methods -- such as the momentum and the RMSprop methods -- are conside
red. The most popular of such accelerated/adaptive optimization methods is
presumably the Adam optimizer due to Kingma & Ba (2014). In this talk we
introduce the notion of the stability region for general deep learning opt
imization methods and we reveal that among standard GD\, momentum\, RMSpro
p\, and Adam we have that Adam is the only optimizer that achieves the opt
imal higher order convergence speed and also has the maximal stability reg
ion. In another main result of this talk\, which we refer to as Adam symme
try theorem\, we show for a simple class of quadratic stochastic optimizat
ion problems (SOPs) that Adam converges\, as the number of Adam steps incr
eases\, to the solution of the SOP (the unique minimizer of the strongly c
onvex objective function) if and only if the random variables in the SOP (
the data in the SOP) are symmetrically distributed. In particular\, in the
standard case where the random variables in the SOP are not symmetrically
distributed we disprove that Adam converges to the minimizer of the SOP a
s the number of Adam steps increases. The talk is based on joint works wit
h Steffen Dereich\, Thang Do\, Robin Graeber\, Sebastian Kassing\, Adrian
Riekert\, and Philippe von Wurstemberger.\n
LOCATION:https://stable.researchseminars.org/talk/cam/102/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Qi Tang (Georgia Tech)
DTSTART:20260601T111500Z
DTEND:20260601T120000Z
DTSTAMP:20260404T094647Z
UID:cam/103
DESCRIPTION:Title: Structure-Preserving Neural Operators for Convection–Diffusion Dyna
mics\nby Qi Tang (Georgia Tech) as part of CAM seminar\n\nLecture held
in MV:L14.\n\nAbstract\nLearning convection–diffusion dynamics with neu
ral operators is difficult because transport and dissipation act on differ
ent scales\, and standard neural operators often lose stability across reg
imes. We propose a Structure-Preserving Neural Operator that captures this
transport–dissipation interplay. The method uses Strang splitting to ev
olve hyperbolic and parabolic dynamics in substeps. Convection is handled
by a learnable semi-Lagrangian approach that follows characteristics and e
mbeds flow structure directly into the architecture\, while diffusion is t
reated through a residual correction neural operator. Experiments on varia
ble-coefficient problems and the Vlasov–Poisson–Fokker–Planck system
show improved stability\, accuracy\, and long-time performance with large
time steps.\n
LOCATION:https://stable.researchseminars.org/talk/cam/103/
END:VEVENT
END:VCALENDAR