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BEGIN:VEVENT
SUMMARY:Shariefuddin Pirzada (University of Kashmir\, India)
DTSTART:20210714T070000Z
DTEND:20210714T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/1
DESCRIPTION:Title: The Laplacian Eigenvalues of Graphs\nby Shariefuddin
Pirzada (University of Kashmir\, India) as part of Combinatorics Today Ser
ies - ITB\n\nAbstract: TBA\n\nShariefuddin PIRZADA\nProfessor\nDepartment
of Mathematics University of Kashmir Srinagar\, Kashmir\, India.\nDean Sch
ool of Physical and Mathematical Sciences\, November 8\, 2017-till date\nH
ead Department of Mathematics\, April 2021-till date\nPreviously\, He taug
ht at King Fahd University of Petroleum and Minerals (2008-2011).\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Oriol Serra (Universitat Politecnica de Catalunya\, Barcelona\, S
pain)
DTSTART:20210810T080000Z
DTEND:20210810T093000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/2
DESCRIPTION:Title: Combinatorial Nullstellensatz\nby Oriol Serra (Univer
sitat Politecnica de Catalunya\, Barcelona\, Spain) as part of Combinator
ics Today Series - ITB\n\n\nAbstract\nThe Combinatorial Nullstellensatz is
an algebraic tool aimed to treat combinatorial problems. After its system
atic set up by Alon at the end of last century the tool has been applied t
o a diversity of problems and some extensions have been explored. In the t
alk\, some chosen examples are given which illustrate particular aspects o
f the application of the method and some of its recent extensions. In part
icular a recent application on counting field colorings in planar graphs w
ill be discussed.\n\nProfessor Oriol SERRA \nDepartment of Mathematics Uni
versitat Polytecnica de Catalunya\, Barcelona Spain. \nCo-Chair Research G
roup of Geometric\, Algebraic and Probabilistic Combinatorics.\n\nVisiting
positions at University of California Santa Cruz (1994-95)\, \nENS Teleco
mmunications Paris (2000)\, \nRenyi Institute Budapest (2001)\, \nCharles
University Prague (2005)\, \nInstitute de Mathmatiques de Bordeaux (2012).
\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ian Wanless (Monash University\, Australia)
DTSTART:20210824T070000Z
DTEND:20210824T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/3
DESCRIPTION:Title: Diagonally Cyclic Latin Squares\nby Ian Wanless (Mona
sh University\, Australia) as part of Combinatorics Today Series - ITB\n\n
\nAbstract\nA Latin square is a square matrix in which each row and column
is a\npermutation of the same set of symbols. Examples include Cayley tab
les\nof finite groups and completed sudoku puzzles. A Latin square is\ndia
gonally cyclic if the symbols occur in cyclic order along each\nbroken dia
gonal parallel to the main diagonal. An example of order 7\, with \none of
its cyclic diagonals highlighted\, is\n\n\\[\n \\left[\n \\begin{array}{c
cccccc}\n 0& 2&\\fbox 5& 1& 6& 4& 3\\\\\n 4& 1& 3&\\fbox 6& 2& 0& 5\\\\\
n 6& 5& 2& 4&\\fbox 0& 3& 1\\\\\n 2& 0& 6& 3& 5&\\fbox 1& 4\\\\\n 5& 3&
1& 0& 4& 6&\\fbox 2\\\\\n \\fbox 3& 6& 4& 2& 1& 5& 0\\\\\n 1& \\fbox 4&
0& 5& 3& 2& 6\\\\\n \\end{array}\n \\right]\n \\]\n\nAn orthomorphism of
an abelian group $G$ is a permutation\n$\\theta:G\\mapsto G$ such that the
map $x\\mapsto\\theta(x)-x$ is also a\npermutation of $G$. It is not hard
to find a bijection between\ndiagonally cyclic Latin squares and orthomor
phisms of cyclic groups.\nI will review the history and applications of di
agonally cyclic Latin\nsquares and orthomorphisms\, including reporting ne
w results of two\ncurrent projects of mine\, one of which is joint with Al
e\\v s Dr\\'apal\n(Charles University\, Prague) and the other is joint wor
k with my student\nJack Allsop.\n\nProfessor Ian WANLESS\nSchool of Mathem
atics\, Monash University\, Australia\n\nAcademic awards and achievements:
\n2017 B.H. Neumann award from the Australian Mathematics Trust\nFor leade
rship\, support and encouragement for mathematics and the\nteaching of mat
hematics at all levels\;\n2009 Medal of the Australian Mathematical Societ
y\nAward for excellence in a researcher under 40 years of age\;\n2008 Hall
Medal from the Institute of Combinatorics and its Applications.\nWorldwid
e award for excellence in a researcher under 40 years of age\;\n2008 Victo
rian Young Tall Poppy Award.\nAwarded by the Australian Institute of Polic
y & Science for research excellence and community engagement\;\n2008 Monas
h University Faculty of Science award for best early career researcher\;\n
2002 Kirkman Medal from the Institute of Combinatorics and its Application
s\,\nWorldwide award for excellence in an early career researcher\;\nJ.G.
Crawford Prize\, 1998 (Best science PhD thesis at ANU in previous year)\;\
nB.H. Neumann Prize\, 40th annual AustMS meeting\, 1996 (best student talk
).\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Akira Saito (Nihon University\, Japan)
DTSTART:20210910T070000Z
DTEND:20210910T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/4
DESCRIPTION:Title: Implications in rainbow forbidden subgraphs\nby Akira
Saito (Nihon University\, Japan) as part of Combinatorics Today Series -
ITB\n\n\nAbstract\nLet $H$ and $H'$ be connected graphs.\nAn edge-colored
graph $G$ is rainbow if each edge receives a different color.\nAlso\,\n$G$
is rainbow $H$-free if $G$ does not contain a rainbow subgraph\nwhich is
isomorphic to $H$.\nIf every rainbow $H'$-free complete graph edge-colored
in sufficiently many colors\nis rainbow $H$-free\,\nwe write $H'\\le H$.\
nMoreover\,\nif $H'$ is a subgraph of $H$\,\nwe write $H'\\subseteq H$\,\n
and if $H'\\subseteq H$ and $H\\ne H'$\,\nwe write $H'\\subsetneq H$. \n\n
It is easy to see that $H'\\subseteq H$ implies $H'\\le H$.\nOn the other
hand\,\nif $H\\subsetneq H'$\,\nthen we naturally do not expect $H'\\le H$
.\nHowever\,\nin $2015$\,\nBass\,\nMagnant\,\nOzeki and Pyron reported $K^
+_{1\,3}\\le K_{1\,3}$\,\nwhere $K_{1\,3}^+$ is the graph\nobtained from $
K_{1\,3}$\nby subdividing one edge with a single vertex.\nSince $K_{1\,3}\
\subseteq K^+_{1\,3}$\,\ntheir result says that even if $H\\subsetneq H'$\
,\n$H'\\le H$ possibly occurs.\n\nIn the former half of the talk\,\nwe fur
ther discuss this possibility.\nWe determine all the pairs $(H\, H')$ with
$H\\subsetneq H'$ and\n$H'\\le H$.\nThis part is a joint work with\nQing
Cu\, Qinghai Liu and Colton Magnant.\n\\par\nIn the latter half\,\nwe give
an overview of the ongoing project to study the pairs $(H\, H')$ with $H'
\\le H$\nwhen neither $H$ nor $H'$ is a subgraph of the other.\nWe will en
counter many strange pairs\,\nwhich suggest that as a binary relation\,\n$
\\le$ is much more complicated\nthan the subgraph relation $\\subseteq$.\n
\nProfessor Akira Saito\, Nihon University\, Japan.\n\nAkira Saito receive
d Bachelor's\, Master's and Doctor's degrees in Science from\nThe Universi
ty of Tokyo in 1981\, 1983 and 1986\, respectively. In 1986\, he started h
is career as an assistant professor at Tohoku University. Then he moved to
Nihon University as a lecturer in 1986. Currently\, he is a professor at
Department of Information Science\, Nihon University.\nHe was a visiting l
ecturer at Otago University\, New Zealand\, in 1988--1989\nand a visiting
professor at The University of Memphis\, U.S.A.\, in 1996--1997.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cheryl Praeger (The University of Western Australia\, Australia)
DTSTART:20210924T063000Z
DTEND:20210924T080000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/5
DESCRIPTION:Title: Codes and designs in Johnson graphs\nby Cheryl Praege
r (The University of Western Australia\, Australia) as part of Combinatori
cs Today Series - ITB\n\n\nAbstract\nThe Johnson graph $J(v\, k)$ has\, as
vertices\, all $k$-subsets of a $v$-set $\\mathcal{V}$\, with two $k$-sub
sets adjacent if and only if they share $k-1$ common elements of $\\mathca
l{V}$. Subsets of vertices of $J(v\, k)$ can be interpreted as the block-
set of an incidence structure\, or as the set of codewords of a code\, and
automorphisms of $J(v\, k)$ leaving the subset invariant are then automor
phisms of the corresponding incidence structure or code. \n \nThis approac
h leads to interesting new designs and codes. For example\, numerous acti
ons of the Mathieu sporadic simple groups give rise to examples of Delandt
sheer designs (which are both flag-transitive and anti-flag transitive)\,
and codes with large minimum distance (and hence strong error-correcting p
roperties).\n \nIn my talk I will explore links between designs and codes
in Johnson graphs which have a high degree of symmetry\, and I will mentio
n several open questions.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chie NARA (Meiji University\, Japan)
DTSTART:20211008T070000Z
DTEND:20211008T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/6
DESCRIPTION:Title: Recent Results in Continuous Flattening Problems of Polyh
edra\nby Chie NARA (Meiji University\, Japan) as part of Combinatorics
Today Series - ITB\n\n\nAbstract\nA. Cauchy used Graph Theory (GT) effect
ively in the proof of his famous theorem “Cauchy’s Rigidity Theorem”
in 1813\, which says that the surface of a convex polyhedron cannot be co
ntinuously transformed to any non-congruent polyhedron if all the faces ar
e rigid. We sometimes encounter the difficulty of describing precise proof
s of facts obtained intuitively and find some ways by applying GT as Cauch
y did. A continuous flattening problem of polyhedra was asked by E. Demain
e et al. in 2001: Can we flatten a polyhedral surface with non-rigid faces
without tearing and stretching? I have been working on this problem more
than a decade. In this talk\, I will introduce several results including r
ecent related works and show where GT is implicitly used. As an applicatio
n of those results\, I will introduce examples of convex polyhedra whose f
aces are rigid except infinitesimally small parts\, which can be continuou
sly flattened.\n\nChie Nara received her BA\, MA\, and Ph.D. degrees in Ma
thematics from the Ochanomizu University in Tokyo. While she worked at Tok
yo City University as a lecturer\, she was offered a scholarship and visit
ed Allen Shield at the University of Michigan as a visiting scholar one ye
ar for the research of the functional analysis. In 2001\, she took a posit
ion at the Tokai University to work in the discrete geometry as well as th
e educational development\, became a professor\, and retired in 2014. Afte
r then\, she has been working at the Meiji University as a visiting resear
cher (professor for two years)\, and her research field has been extended
to the Origami engineering\, added to the discrete geometry. She translate
d a famous book “Introduction to Graph Theory with Applications” by Bo
ndy and Murty into Japanese in 1991 and wrote a book “Origami Science”
published in 2019.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Peter Cameron (University of St Andrews\, United Kingdom)
DTSTART:20211022T080000Z
DTEND:20211022T093000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/7
DESCRIPTION:Title: Graphs defined on groups\nby Peter Cameron (Universit
y of St Andrews\, United Kingdom) as part of Combinatorics Today Series -
ITB\n\n\nAbstract\nThere has been a lot of recent interest on graphs whose
vertex set is a group G and whose edges reflect the structure of G: examp
les include the commuting graph\, the generating graph\, and the power gra
ph. It is possible to arrange these graphs in a hierarchy\, and compare th
eir properties\, as well as look at properties of the differences between
successive graphs in the hierarchy.\n\nI was born in Toowoomba\, Australia
\, and studied at the University of Queensland and Oxford University\, tak
ing my DPhil at Oxford under the supervision of Peter Neumann. After a pos
tdoc\, I held teaching positions in Oxford and then Queen Mary University
of London\, where I retired in 2012. Since then I have been a half-time pr
ofessor at the University of St Andrews (Scotland's oldest university). I
work mostly in group theory and combinatorics: my real interest is groups
acting on structures of various kinds\, but I also have worked in model th
eory and (briefly) in mathematical psychology. I have over 300 publication
s and have supervised around 40 PhD students. Awards include the Senior Wh
itehead Prize from the London Mathematical Society and the Euler medal fro
m the Institute for Combinatorics and its Applications.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Martin Grohe (RWTH AACHEN University\, Germany)
DTSTART:20211119T070000Z
DTEND:20211119T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/8
DESCRIPTION:Title: The Logic of Graph Neural Networks\nby Martin Grohe (
RWTH AACHEN University\, Germany) as part of Combinatorics Today Series -
ITB\n\n\nAbstract\nGraph neural networks (GNNs) are a deep learning archit
ecture for graph structured data that has developed into a method of choic
e for many graph learning problems in recent years. It is therefore import
ant that we understand their power. One aspect of this is the expressivene
ss: which functions on graphs can be expressed by a GNN model? Surprisingl
y\, this question has a precise answer in terms of logic and a combinatori
al algorithm known as the Weisfeiler Leman algorithm.\n\nMy talk will be a
survey of recent results linking the expressiveness of\nGNNs to logical e
xpressivity.\n\nMartin Grohe is a Professor for Theoretical Computer Scien
ce at the RWTH Aachen. He received his PhD in Mathematics at Freiburg Univ
ersity in 1994 and then spent a year as a visiting scholar at Stanford and
the University of California at Santa Cruz. Before joining the Department
of Computer Science of RWTH Aachen in 2012\, he held positions at the Uni
versity of Illinois at Chicago\, the University of Edinburgh\, and the Hum
boldt University at Berlin.\n\nHis research interest are in theoretical co
mputer science interpreted broadly\, including logic\, algorithms and comp
lexity\, graph theory\, theoretical aspects of machine learning\, and data
base theory.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tom Kelly (University of Birmingham\, United Kingdom)
DTSTART:20211126T080000Z
DTEND:20211126T093000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/9
DESCRIPTION:Title: Coloring hypergraphs of small codegree\, and a proof of t
he Erdős–Faber–Lovász conjecture\nby Tom Kelly (University of Bi
rmingham\, United Kingdom) as part of Combinatorics Today Series - ITB\n\
n\nAbstract\nThe theory of edge-coloring hypergraphs has a rich history wi
th important connections and application to other areas of combinatorics e
.g. design theory and combinatorial geometry. A long-standing problem in
the field is the Erdős–Faber–Lovász conjecture (posed in 1972)\, whi
ch states that the chromatic index of any linear hypergraph on n vertices
is at most n. In joint work with Dong Yeap Kang\, Daniela Kühn\, Abhishe
k Methuku\, and Deryk Osthus\, we proved this conjecture for every suffici
ently large n. Recently\, we also solved a related problem of Erdős from
1977 on the chromatic index of hypergraphs of small codegree. In this ta
lk\, I will survey the history behind these results and discuss some aspec
ts of the proofs.\n\nTom Kelly received his Bachelor's degree from Princet
on University in 2015\, where he was awarded the Middleton Miller '29 priz
e for best independent work in mathematics. He then obtained his PhD in C
ombinatorics & Optimization from the University of Waterloo in 2019\, wher
e he was awarded the first-place Mathematics Doctoral Prize and was a Univ
ersity Finalist for the Governor General's Gold Medal. He is currently a
Research Fellow at the University of Birmingham.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Catherine Greenhill (University of New South Wales\, Australia)
DTSTART:20211210T070000Z
DTEND:20211210T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/10
DESCRIPTION:Title: Results about random hypergraphs\, proved using asymptot
ic enumeration formulae\nby Catherine Greenhill (University of New Sou
th Wales\, Australia) as part of Combinatorics Today Series - ITB\n\n\nAbs
tract\nHypergraphs are generalisations of graphs\, where each edge is a su
bset of the vertex set. In a uniform hypergraph\, every edge has the same
size: for example\, a graph is a 2-uniform hypergraph. Asymptotic enumerat
ion involves finding an approximate formula for a combinatorial set\, such
as the number of hypergraphs with given properties. The formula has a rel
ative error that gets smaller as the number of vertices grows. As well as
being interesting in their own right\, these formulae can be very useful
tools which can help us prove results about random hypergraphs\, or analys
e randomised algorithms for hypergraphs. I will illustrate this by describ
ing how my co-authors and I have used asymptotic enumeration formulae to p
rove three very different results involving hypergraphs:\n(1) One result i
s the analysis of an algorithm for randomly generating uniform hypergraphs
with a given degree sequence\;\n(2) Another result describes the degree d
istribution of a random uniform hypergraph with a given number of edges\;\
n(3) Another result establishes a threshold for the existence of a 2-facto
r (spanning 2-regular subhypergraph) in random regular uniform hypergraphs
.\n\nCatherine Green hill is a professor at the School of Mathematics and
Statistics\, University of New South Wales\, Australia. She was awarded th
e 2015 Christopher Heyde Medal in Pure Mathematics by the Australian Acade
my of Science and the 2010 Hall Medal by the Institute of Combinatorics an
d its Applications.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Camino Balbuena (Universitat Politecnica de Catalunya\, Spain)
DTSTART:20220128T070000Z
DTEND:20220128T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/11
DESCRIPTION:Title: Moore Cages of Girth 8\nby Camino Balbuena (Universi
tat Politecnica de Catalunya\, Spain) as part of Combinatorics Today Serie
s - ITB\n\n\nAbstract\nIn this talk we explain some problems related with
graphs called cages of girth\n8. These graphs are regular\, have girth 8\,
and have the least possible number of vertices.\nThe lower bound on this
value is easy to obtain\, and the cages with order equal to the lower\nbou
nd are called Moore cages of girth 8. We will give an algebraic descriptio
n of Moore\n$(q+1\,8)$-cages\, where $q \\geq 2$ denotes a prime power. St
arting of this description we will\nexplain how to obtain graphs of girth
8 and degrees $q$ or $q-1$ having the minimum number\nof vertices known un
til now. Also the algebraic description of Moore $(q+1\,8)$-cages allows\n
us to obtain $k$-regular graphs of girth $7$ having the minimum number of
vertices known until\nnow.\n\nProf Camino Balbuena:\nIn 1989 she joined th
e Universitat Politecnica de Catalunya and in 1995 she received the Phd de
gree from the same university. Since then she has been working with the Re
search Group on Combinatorics\, Graph Theory and Applications (COMBGRAF).
Her research is focused on Fault-Tolerance of networks and the constructio
n of extremal graphs with prescribed parameters. Most of her research is c
oncerned to the study of conditional connectivity and particularly on the
restricted edge connectivity of graphs and digraphs.\n\nOne remarkable con
tribution that she has made is the best known breakthrough in the solution
of the conjecture claiming that cages are maximally connected by proving
for odd girth that the connectivity is at least the degree divided by two.
The study of cages produced the need to obtain these objects more easily.
She has given a direct way for obtaining the adjacency matrix of any proj
ective plane of order a prime power\, which is equivalent to obtain cages
of girth 6. Moreover\, she and her collaborators have given a simple formu
la for obtaining generalized quadrangles or equivalently cages of girth 8.
This knowledge has allowed to solve other related problems as the followi
ng:\n• To construct the smallest known graphs of girth 5.\n• To prove
a conjecture about the construction of regular graphs with a given girth-p
air having the small number of vertices.\n• To find a family of graphs f
ree of short cycles having m ximum number of edges.\n• To characterize
bipartite graphs of girth 6 having a (1\,≤𝑙𝑙)−Code and a good c
ontribution in the study of graphs of girth 5 having an identifying code.\
nIt deserves also to highlight that she and her collaborators have done a
very good advance in the conjecture claiming that any tree is graceful by
proving that an infinite family of trees is graceful.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nobuaki Obata (Tohoku University\, Japan)
DTSTART:20220218T070000Z
DTEND:20220218T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/12
DESCRIPTION:Title: Quadratic Embedding Constants of Graphs and Related Topi
cs\nby Nobuaki Obata (Tohoku University\, Japan) as part of Combinator
ics Today Series - ITB\n\n\nAbstract\nThe quadratic embedding (QE) constan
t of a finite \nconnected graph $G$\, denoted by $\\mathrm{QEC}(G)$\,\nis
by definition the maximum of the quadratic function \nassociated to the di
stance matrix on a certain sphere \nof codimension two. The QE constant wa
s introduced \naround 2018 by the speaker and has been expected to\nbe an
interesting invariant of finite connected graphs.\nIn this lecture I will
survey basic results on the QE constant\,\ndiscuss some related topics and
propose some questions.\n\nProf. Nobuaki Obata from Tohoku University Jap
an.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xueliang Li (Nankai University\, China)
DTSTART:20220408T070000Z
DTEND:20220408T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/13
DESCRIPTION:Title: Extremal Problems for Graphical Function-Indices and f-W
eighted Adjacency Matrices\nby Xueliang Li (Nankai University\, China)
as part of Combinatorics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hao Huang (NUS\, Singapore)
DTSTART:20220423T070000Z
DTEND:20220423T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/14
DESCRIPTION:Title: Interlacing Methods in Extremal Combinatorics\nby Ha
o Huang (NUS\, Singapore) as part of Combinatorics Today Series - ITB\n\nA
bstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eiichi Bannai (Kyushu University\, Japan)
DTSTART:20220625T070000Z
DTEND:20220625T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/15
DESCRIPTION:Title: Explicit Construction of Exact Unitary Designs\nby E
iichi Bannai (Kyushu University\, Japan) as part of Combinatorics Today Se
ries - ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Brendan McKay (ANU\, Australia)
DTSTART:20220728T070000Z
DTEND:20220728T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/16
DESCRIPTION:Title: Ramsey Theory and Ramsey Numbers\nby Brendan McKay (
ANU\, Australia) as part of Combinatorics Today Series - ITB\n\nAbstract:
TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stanislaw Radziszowski (Rochester Isntitute of Technology\, USA)
DTSTART:20220825T120000Z
DTEND:20220825T133000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/17
DESCRIPTION:Title: More on Computational Approach in Ramsey Theory\nby
Stanislaw Radziszowski (Rochester Isntitute of Technology\, USA) as part o
f Combinatorics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Linda Lesniak (Western Michigan University\, USA)
DTSTART:20220909T120000Z
DTEND:20220909T133000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/18
DESCRIPTION:Title: On the Necessity of Chvatal's Hamiltonian Degree Conditi
on and Forcibly P Degree Conditions\nby Linda Lesniak (Western Michiga
n University\, USA) as part of Combinatorics Today Series - ITB\n\n\nAbstr
act\nIn 1972 Chvatal gave a well-known sufficient condition for a graphica
l sequence to be forcibly hamiltonian\, and showed that in some sense his
condition is best possible. Even though\, for each $n \\geq 3$\, we have c
onstructed exponentially many forcibly hamiltonian $n$-sequences that do n
ot satisfy Chvatal’s condition\, in this talk we will discuss why we con
jecture that the proportion of forcibly hamiltonian $n$-sequences that sat
isfy Chvatal’s condition approaches 1 exponentially fast. Informally\, w
ith probability approaching 1 as $n \\rightarrow 1$\; we conjecture that a
graphical $n$-sequence $\\pi$ is forcibly hamiltonian if and only if $\\p
i$ satisfies Chvatal’s condition. In contrast\, we can essentially prove
that for every $k \\geq 1$ the sufficient condition of Bondy and Boesch f
or forcible $k$-connectedness is not necessary in the same way. This sugge
sts a more general question for other monotone graphical properties $P$ th
at we will discuss here.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Akihiro Munemasa (Tohoku University\, Japan)
DTSTART:20220929T070000Z
DTEND:20220929T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/19
DESCRIPTION:Title: Sphere Packings\, Root Systems and Signed Graphs\nby
Akihiro Munemasa (Tohoku University\, Japan) as part of Combinatorics Tod
ay Series - ITB\n\n\nAbstract\nIn 1981 Bannai and Sloane proved the unique
ness of optimal configurations on the spheres in the Euclidean spaces of d
imension 8 and 24. For the dimension 8\, the set of 240 vectors of the roo
t system of type $E_8$ was shown to be the unique largest subset of the sp
here in which two vectors are at least 60 degrees apart. A slice of the ro
ot system of type $E_8$ contains a set of 28 equiangular lines in the 7-di
mensional hyperplane. In 2021\, based on joint work with Cao\, Koolen and
Yoshino\, we showed that this set is characterized as the unique strongly
maximal set of equiangular lines in the sense that no more lines can be ad
ded even if the dimension is allowed to increase. In this talk\, we propos
e a framework to capture in a similar manner the slice of the 24-dimension
al configuration\, that is\, the set of 2300 lines determined by the short
er Leech lattice.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicholas Wormald (Monash University\, Australia)
DTSTART:20221013T070000Z
DTEND:20221013T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/20
DESCRIPTION:Title: Uniform generation of combinatorial objects\nby Nich
olas Wormald (Monash University\, Australia) as part of Combinatorics Toda
y Series - ITB\n\n\nAbstract\nIt can be useful to sample from a class of o
bjects uniformly at random\, for instance in order to test algorithms. Th
is can be easy if the objects can be counted in appropriate ways. Even app
roximate counts can be sometimes be used for exactly uniform sampling\, fo
r instance via rejection sampling. We discuss a family of algorithms that
are useful for generating random graphs with given degrees\, and related s
tructures such as Latin rectangles and statistical contingency tables. The
se algorithms achieve a precisely uniform distribution and can be implemen
ted so as to run in essentially optimal time provided that the objects bei
ng generated are not very "dense".\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Edy Tri Baskoro (Institut Teknologi Bandung\, Indonesia)
DTSTART:20221029T070000Z
DTEND:20221029T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/21
DESCRIPTION:Title: On the Existence of Almost Moore Digraphs\nby Edy Tr
i Baskoro (Institut Teknologi Bandung\, Indonesia) as part of Combinatoric
s Today Series - ITB\n\n\nAbstract\nFor any integers $d \\geq 2$ and $k \\
geq 1$\, an almost Moore digraph is defined as a diregular digraph of degr
ee $d$\, diameter $k$ and order $d+d^2+ \\cdots + d^k$. The question of it
s existence has attracted a lot of attention. For some small values of $d$
and $k$ we have known the answer\, but for other cases the question remai
ns open. The structural study on these digraphs (if they exist) was initia
ted by the work of Mirka Miller by introducing a repeat function. In this
talk\, we will discuss the beauty of repeat function used to explore the p
ossibility of the existence of almost Moore digraphs.\n\nEdy Tri Baskoro w
as born in Jombang\, Indonesia\, received his a B.Sc degree in mathematics
from Institut Teknologi Bandung (ITB) Indonesia in 1987\, his Master degr
ee from University of New England Australia in 1992\, and his PhD degree f
rom the University of Newcastle\, Australia in 1996. Since then he has hel
d a senior academic position at ITB. Since July 2006\, he has been honoure
d a professor in mathematics of ITB. He served as the Dean of Faculty of
Mathematics and Natural Sciences\, Institut Teknologi Bandung 2015-2019. H
e has been acknowledged as an adjunct professor at the University of Newca
stle Australia 2006-2015 and the Abdus Salam School of Mathematical Scienc
es\, GC University\, Lahore Pakistan 2006-2015. Currently\, he serves as a
chair of the Professor Forum of ITB. \n\nHis main research interests are
graph theory and combinatorics. He is a pioneer in the development of grap
h theory and combinatorics community in Indonesia. For his leadership\, he
was elected as the President of Indonesian Combinatorial Mathematics Soci
ety (2006-2013). For his contributions to these fields he has been awarded
Habibie Award in Basic Science Research (2009)\, Australian Alumni Award
for Excellence in Education (2009)\, and the Extraordinary Intellectual Qu
ality Award (2010). He was appointed as the President of Indonesian Mathem
atical Society (2006-2008). He also plays a significant role in the develo
pment of mathematics in South East Asia region. He was the President of So
utheast Asian Mathematical Society (2014-2015)\, and served as a member of
Scientific Committee of International Center for Pure and Applied Mathema
tics (CIMPA) in 2009- 2020. \n\nHe has also contributed to the developmen
t of national standards for education from primary school to higher educat
ion in Indonesia as the member of the Board of National Standards for Educ
ation since 2005 until 2015. He has been conducting various international
conferences in mathematics and sciences. As of October 2022\, he has had t
he Scopus h-index 19 with 175 research papers published in international j
ournals/proceedings with 1475 citations\, and produced more than 28 PhD gr
aduates.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sang-il Oum (Institute for Basic Science and KAIST\, South Korea)
DTSTART:20221111T020000Z
DTEND:20221111T033000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/22
DESCRIPTION:Title: Building the hierarchy of graph classes\nby Sang-il
Oum (Institute for Basic Science and KAIST\, South Korea) as part of Combi
natorics Today Series - ITB\n\n\nAbstract\nWe will survey the classificati
on of graph classes in terms of the transductions in monadic second-order
logic. Blumensath and Courcelle (2010) characterized that every class of g
raphs is equivalent by transductions of the monadic second-order logic of
the second kind to one of the following: class of all trees of height n fo
r an integer n\, class of all trees\, class of all paths\, and class of al
l grids. They conjectured that there is a similar linear hierarchy of grap
h classes in terms of the monadic second-order logic of the first kind. We
will discuss how a recent theorem of the speaker with O-joung Kwon\, Rose
McCarty\, and Paul Wollan (2019) on the vertex-minor obstruction for shru
b-depth and a theorem of the speaker with Bruno Courcelle (2007) on graphs
of large rank-width and logical expression of vertex-minors solve some su
bproblems of their conjecture.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicolas Trotignon (CNRS\, LIP\, ENS de Lyon\, France)
DTSTART:20221124T070000Z
DTEND:20221124T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/23
DESCRIPTION:Title: Widths and even-hole-free graphs\, a tour in structural
graph theory\nby Nicolas Trotignon (CNRS\, LIP\, ENS de Lyon\, France)
as part of Combinatorics Today Series - ITB\n\n\nAbstract\nEven-hole-free
graphs play an important role in the history of structural graph theory.
In particular\, the attempts made by Cornuéjols\, Conforti and Vuskovic (
among others) to describe their structure in the 1990’s finally led to t
he right conjecture about the structure of perfect graphs\, that was prove
d by Chudnovsky\, Robertson\, Seymour and Thomas in 2002. Today\, the stru
cture of even-hole-free graphs and perfect graphs is still far from being
fully understood. In this talk\, we will survey several attempts to study
their structure through classical width parameters\, such as treewidth. It
turns out that these attempts led to several conjectures and theorems abo
ut an « induced subgraph » version of the celebrated grid theorem of Rob
ertson and Seymour.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Csilla Bujtás (University of Ljubljana\, Ljubljana\, Slovenia)
DTSTART:20221216T070000Z
DTEND:20221216T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/24
DESCRIPTION:Title: Triangle packings and coverings\nby Csilla Bujtás (
University of Ljubljana\, Ljubljana\, Slovenia) as part of Combinatorics T
oday Series - ITB\n\n\nAbstract\nIn a graph $G$\, a triangle packing is a
set of pairwise edge-disjoint triangles\, and a triangle covering is a set
of edges the removal of which makes the graph triangle-free. The maximum
size $\\nu_\\Delta(G)$ of a triangle packing and the minimum size $\\tau_\
\Delta(G)$ of a triangle covering clearly satisfies $\\tau_\\Delta\\left(G
\\right)\\le3\\nu_\\Delta(G)$. Tuza’s 40-year-old conjecture says that t
he stronger statement $\\tau_\\Delta\\left(G\\right)\\le2\\nu_\\Delta(G)$
is also valid for all graphs. This relation holds with equality for the co
mplete graphs $K_4$ and $K_5$. Moreover\, for every positive $\\epsilon$ t
here exists a $K_4$-free graph $G$ with $\\tau_\\Delta(G)\\ >\\ \\left(2-
\\epsilon\\right)\\nu_\\Delta(G)$.\nThe problem was extensively studied\,
and the inequality has been proved over several important graph classes. H
owever\, the general conjecture is still wide open. In the talk\, we surve
y the earlier results and discuss some recent ones concentrating on the cl
ass of $K_4$-free graphs.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sanming Zhou (The University of Melbourne\, Australia)
DTSTART:20230217T070000Z
DTEND:20230217T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/25
DESCRIPTION:Title: Nowhere-zero 3-flows in vertex-transitive graphs\nby
Sanming Zhou (The University of Melbourne\, Australia) as part of Combina
torics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hilda Assiyatun (Institut Teknologi Bandung\, Indonesia)
DTSTART:20230331T070000Z
DTEND:20230331T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/26
DESCRIPTION:Title: On Ramsey-minimal graphs for combinations containing mat
chings\, paths or stars\nby Hilda Assiyatun (Institut Teknologi Bandun
g\, Indonesia) as part of Combinatorics Today Series - ITB\n\nAbstract: TB
A\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Kral (Masaryk University\, Czech Republic)
DTSTART:20230411T070000Z
DTEND:20230411T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/27
DESCRIPTION:Title: Quasirandom combinatorial structures\nby Daniel Kral
(Masaryk University\, Czech Republic) as part of Combinatorics Today Seri
es - ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gordon Royle (University of Western Australia\, Australia)
DTSTART:20230608T070000Z
DTEND:20230608T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/28
DESCRIPTION:Title: Hamilton cycles in cubic and other graphs\nby Gordon
Royle (University of Western Australia\, Australia) as part of Combinator
ics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marien Abreu (Università degli Studi della Basilicata - Potenza\,
Italy)
DTSTART:20230707T070000Z
DTEND:20230707T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/29
DESCRIPTION:Title: Extending perfect matchings to Hamiltonian cycles\nb
y Marien Abreu (Università degli Studi della Basilicata - Potenza\, Italy
) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nA graph G\, a
dmitting a perfect matching\, in which every perfect matching can be exten
ded to a Hamiltonian cycle is said to be Perfect-Matching-Hamiltonian (PMH
for short). Consider the complete graph KG with the same vertex set as G.
A perfect matching of KG is called a pairing of G. If for every paring M
of G there exists a perfect matching N of G such that M ∪ N is a hamilto
nian cycle of KG we say that G is Pairing-Hamiltonian (PH for short). Note
the subtle difference between extending a pairing\, instead of a perfect
matching of G\, to a hamiltonian cycle using only edges of G. A PMH graph
is thus a special case of a PH graph. Results about these two families of
graphs\, although named differently\, date back to the 1970’s when Las V
ergnas and Haggkvist found Ore-type conditions for a graph to be PMH. Also
\, all hypercubes Qd\, for d ≥ 2 were shown to be PH\, by Fink in 2007\,
thus proving a stronger version of a conjecture by Kreweras\, which state
d that hypercubes are PMH. Moreover cubic PH graphs were characterized\, i
n 2015\, to be only K4\, K3\,3 and the cube Q3\, by Alahmadi et al. This s
eminar contains resent results on PMH and PH graphs that can be summarized
into: (i) Graphs for which the line graph is PMH\, (ii) Cubic graphs whi
ch are PMH\, and (iii) Products of graphs which are PH.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:M. Salman\, A.N. (Institut Teknologi Bandung\, Indonesia)
DTSTART:20230818T070000Z
DTEND:20230818T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/30
DESCRIPTION:Title: THE LOCATING RAINBOW CONNECTION NUMBER OF GRAPHS\nb
y M. Salman\, A.N. (Institut Teknologi Bandung\, Indonesia) as part of Com
binatorics Today Series - ITB\n\n\nAbstract\nLet G=(V(G)\,E(G)) be a finit
e and connected graph of order n≥2. In 2021\, we introduced the locating
rainbow connection number of G\, denoted by rvcl(G)\, that combines the c
oncepts of the rainbow vertex coloring and the partition dimension of a gr
aph. In this talk\, we present some results about it. Firstly\, we provide
both a lower bound and an upper bound for rvcl(G). Then\, we characterize
the graphs G with rvcl(G)=2 or rvcl(G)=n. Furthermore\, we determine the
locating rainbow connection number of some graph classes\, including comp
lete graphs\, paths\, stars\, regular bipartite graphs\, and trees. Additi
onally\, we present the locating rainbow connection number of amalgamation
of complete graphs. In the last section\, we present some open problems.\
n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jose Maria Balmaceda (University of the Philippines Diliman\, Phil
ippines)
DTSTART:20230930T070000Z
DTEND:20230930T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/31
DESCRIPTION:Title: Association Schemes and Related Structures\nby Jose
Maria Balmaceda (University of the Philippines Diliman\, Philippines) as p
art of Combinatorics Today Series - ITB\n\n\nAbstract\nAssociation schemes
\, first introduced in the 1950s by R.C. Bose and T. Shimamoto in the desi
gn of experiments\, are combinatorial objects that were used by P. Delsart
e in the 1970s to study coding theory and design theory. Today they are im
portant structures in algebraic combinatorics and the theory offers a unif
ying framework for the study of various objects such as finite geometries\
, graphs with high symmetry\, codes\, and designs. We give an introduction
to the theory of association schemes\, including its sources and connecti
ons with other branches of math. We also present some recent work on the e
xtension of the classical theory to association schemes on triples\, where
underlying relations and corresponding adjacency algebras are ternary ins
tead of binary.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mihyun Kang (Graz University of Technology\, Institute of Discret
e Mathematics\, Graz\, Austria)
DTSTART:20231020T070000Z
DTEND:20231020T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/32
DESCRIPTION:Title: Topological aspects of random graphs\nby Mihyun Kang
(Graz University of Technology\, Institute of Discrete Mathematics\, Gra
z\, Austria) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nIn
this talk we will briefly overview classical results on Erdos-Renyi rando
m graphs and discuss various topological aspects of random graphs. We are
interested in the following questions: How does the genus of a random grap
h change as the edge density increases? How does a topological constraint
(such as being planar) influence the global and local structure of a rando
m graph (such as the order of the largest component and local weak limits)
?\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kiki Ariyanti Sugeng (Universitas Indonesia\, Indonesia)
DTSTART:20231103T070000Z
DTEND:20231103T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/33
DESCRIPTION:Title: On Modular Irregularity Strength for Some Families of Gr
aphs\nby Kiki Ariyanti Sugeng (Universitas Indonesia\, Indonesia) as p
art of Combinatorics Today Series - ITB\n\n\nAbstract\nLet consider a simp
le and finite graph $G$ with order $n$. Motivated by irregular graph\, Cha
rtrand {\\it et al.} in 1998 defined an irregular labeling as an edge $k$-
labeling $f: E(G) \\to \\{1\, 2\, ... \, k\\}$\, for a positive integer $
k$\, so that every vertex has different weight. The sum of all edge labels
which is incidence to $v$ is called the vertex weight of $v$. What are we
looking for is the minimum number $k$ for this kind of labeling. The mini
mum number of $k$ for such labeling is called the irregularity strength of
a graph G and is denoted by s(G). In 2020\, Baca et al.introduced the var
iation of irregular labeling in modular version. Modular irregular labelin
g of a graph $G$ is an edge $k$-labeling $f: E(G)\\to \\{1\,2\,...\,k\\}$
such that the modular weight\, which is the sum of all edges that incident
to $v$ modulo $n$\, of all vertices are all different. For the case of mo
dular\, the modular irregularity strength of a graph $G$\, notated by ms($
G$)\, is a minimum number $k$ such that a graph $G$ has modular irregular
labeling with the largest label $k$. In this talk\, we give the survey on
which families of graphs that have been proved that have modular irregular
ity labeling.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sandi Klavzar (University of Ljubljana\, Slovenia)
DTSTART:20231117T070000Z
DTEND:20231117T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/34
DESCRIPTION:Title: Visibility Concepts in Graph Theory\nby Sandi Klavza
r (University of Ljubljana\, Slovenia) as part of Combinatorics Today Seri
es - ITB\n\n\nAbstract\nRecently\, the field of computer science has seen
a need to explore the concept of visibility in graph theory. The variety o
f related concepts can be described as follows. Given a connected graph $G
$ and a set of vertices $X\\subseteq V(G)$\, two vertices $x\,y\\in V(G)$
are called to be $X$-\\emph{visible} if there is a shortest $x\,y$-path (a
lso called geodesic) whose interior vertices do not belong to $X$. With th
is idea in mind\, we say that $X$ is \n \n\n(1) a mutual-visibility set: i
f any two vertices of $X$ are $X$-visible\; \n(2) an outer mutual-visibili
ty set: if any two vertices $x\,y\\in X$ and any two vertices $x\\in X$ an
d $y\\in \\overline{X}$ are $X$-visible\; \n(3) a dual mutual-visibility s
et: if any two vertices $x\,y\\in X$ and any two vertices $x\,y\\in \\over
line{X}$ are $X$-visible\; and \n(4) a total mutual-visibility set: if any
two vertices $x\,y\\in V(G)$ are $X$-visible.\n\nIn this talk\, we will p
resent some results on these concepts. We will pay special attention to Ha
mming graphs\, since problems on them give rise to unexpected connections
with some classical mathematical problems and concepts.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vida Dujmovic (University of Ottawa\, Canada)
DTSTART:20231208T120000Z
DTEND:20231208T133000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/35
DESCRIPTION:Title: Proof of the Clustered Hadwiger Conjecture\nby Vida
Dujmovic (University of Ottawa\, Canada) as part of Combinatorics Today Se
ries - ITB\n\n\nAbstract\nHadwiger's Conjecture asserts that every Kh-mino
r-free graph is properly (h-1)-colourable. We prove the following improper
analogue of Hadwiger's Conjecture: for fixed h\, every Kh-minor-free grap
h is (h-1)-colourable with monochromatic components of bounded size. The n
umber of colours is best possible regardless of the size of monochromatic
components. It solves an open problem of Edwards\, Kang\, Kim\, Oum and Se
ymour [SIAM J. Disc. Math. 2015]\, and concludes a line of research initia
ted in 2007.\n\n\nThis is joint work with Louis Esperet\, Pat Morin and Da
vid R. Wood.\n\nVida Dujmovic is a University Research Chair and Professor
of Computer Science at University of Ottawa. Her main research areas are
graph theory (geometric and structural). She has published over 80 journal
papers. \n\nShe is a recipient of the Early Researcher Award by the Onta
rio government\, Glinski Award for Excellence in Research by the Universit
y of Ottawa. She is an invited speaker at the 2024 European Congress of M
athematicians\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Djoko Suprijanto (Institut Teknologi Bandung)
DTSTART:20240224T070000Z
DTEND:20240224T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/36
DESCRIPTION:Title: Cyclic codes over finite rings and their generalizations
: Structural properties and applications\nby Djoko Suprijanto (Institu
t Teknologi Bandung) as part of Combinatorics Today Series - ITB\n\n\nAbst
ract\nCyclic codes are one of the most widely studied families of codes\,
both because of their rich mathematical structure and their use in applica
tions. Cyclic codes have also been generalized in numerous ways\, includin
g negacyclic codes\, constacyclic codes\, and skew cyclic codes with deriv
ation.\n\nIn this talk\, we will discuss recent developments in the study
of cyclic codes and their generalization\, with a focus on what we call tw
o-step generalizations of cyclic codes\, or skew cyclic codes with derivat
ion.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Charles Joseph Colbourn (Arizona State University\, USA)
DTSTART:20240511T020000Z
DTEND:20240511T033000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/37
DESCRIPTION:Title: Popularity Labellings for Steiner Systems\nby Charle
s Joseph Colbourn (Arizona State University\, USA) as part of Combinatoric
s Today Series - ITB\n\n\nAbstract\nSteiner systems and their duals are wi
dely used for data layout in distributed storage systems. In practice\, ma
pping data items to storage units often ignores the long-term popularity o
f the items\, which can cause a significant imbalance in traffic to storag
e units. In addressing popularity\, two main problems arise:\n\n1. Label t
he v points of a design with {0\, 1\, ...\, v−1}\, computing each block
sum as the sum of the labels of points contained in that block. The block
difference sum is the difference between the largest and smallest block su
ms. Popularity point labelling seeks to minimize the block difference sum.
\n\n2. Label the b blocks of a design with {0\, 1\, ...\, b − 1}\, comp
uting each point sum as the sum of the labels of blocks containing that po
int. The point difference sum is the difference between the largest and sm
allest point sums. Popularity block labelling seeks to minimize the point
difference sum.\n\nWe first derive lower bounds on the difference sums for
Steiner systems S(t\, k\, v). We then outline constructions that yield
‘small’ difference sums. Finally\, we mention some open problems that
deserve more attention.\n\nBrief biography: Charles J. Colbourn was born i
n Toronto in 1953. He completed his B.Sc. (Toronto)\, M.Math. (Waterloo)\
, and Ph.D. (Toronto)\, all in computer science. He held faculty position
s at the University of Saskatchewan\, the University of Waterloo\, and the
University of Vermont\, and has been a Professor of Computer Science and
Engineering at Arizona State University since 2001.\n\nHe is co-editor of
the Handbook of Combinatorial Designs and author of Triple Systems and The
Combinatorics of Network Reliability. He is an editor-in-chief of the Jo
urnal of Combinatorial Designs. His research concerns applications of com
binatorial designs in networking\, computing\, and communications.\n\nFor
more information\, see https://www.public.asu.edu/}$\\sim${\\tt ccolbou/\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cristina Dalfo (Universitat de Lleida Igualada (Barcelona)\, Catal
onia)
DTSTART:20241125T070000Z
DTEND:20241125T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/38
DESCRIPTION:Title: Combined voltage assignments\, factored lifts\, and thei
r spectra\nby Cristina Dalfo (Universitat de Lleida Igualada (Barcelon
a)\, Catalonia) as part of Combinatorics Today Series - ITB\n\n\nAbstract\
nIn this talk\, we introduce the concept of factored lift\, associated wit
h a combined voltage graph\, as a generalization of the lift graph. We pre
sent a new method for computing all the eigenvalues and eigenspaces of fac
tored lifts. The underlying group can be Abelian or not Abelian\, and we w
ill deal with both cases.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hajime Tanaka (Tohoku University\, Japan)
DTSTART:20241104T090000Z
DTEND:20241104T103000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/39
DESCRIPTION:Title: Linear/semidefinite programming techniques in combinator
ics\nby Hajime Tanaka (Tohoku University\, Japan) as part of Combinato
rics Today Series - ITB\n\n\nAbstract\nLinear/semidefinite programming tec
hniques have been useful in proving theorems in various areas of combinato
rics\, such as coding theory and extremal set theory. While they do not al
ways lead to the best versions\, these techniques provide attractive appli
cations of algebraic graph theory.\n\nIn this talk\, I will begin with the
fundamental results by Delsarte and Lovász in the 1970's and then move o
n to discussing some of the most successful applications\, an example of w
hich is Wilson's 1984 proof of the Erdős-Ko-Rado theorem. I will also men
tion recent joint work with Norihide Tokushige on a measure version of the
q-analog of this theorem.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ismael G. Yero (University of Cadiz Algeciras Campus\, Spain)
DTSTART:20241209T090000Z
DTEND:20241209T103000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/40
DESCRIPTION:Title: Mobile Mutual-Visibility Sets in Graphs\nby Ismael G
. Yero (University of Cadiz Algeciras Campus\, Spain) as part of Combinat
orics Today Series - ITB\n\n\nAbstract\nGiven a connected graph $G$\, a mu
tual-visibility set of G is a set of vertices $S \\subset V(G)$ such that
for each two vertices $x\,y$ in $S$ there is a shortest $(x\,y)$-path whos
e interior vertices are not in $S$. Assume now that in each vertex of a mu
tual-visibility set $S$ a robot is placed\, and consider that they can mov
e from one vertex to a neighboring one\, so that at each stage only one ro
bot moves to a neighbor of it. The set $S$ is called a mobile mutual-visib
ility set of $G$\, if there exists a sequence of moves of the robots such
that each vertex of $G$ is visited by at least one robot\, while all the t
ime\, the set of vertices occupied by the robots is a mutual-visibility se
t of $G$. The mobile mutual-visibility number of $G$ is the cardinality of
a largest mobile mutual-visibility set of $G$. Several contributions in
these notions shall be presented in this talk. The results of the work are
from the article [M. Dettlaff\, M. Lemanska\, J. A. Rodriguez-Velazquez\,
I. G. Yero\, Mobile mutual-visibility sets in graph. Manuscript\, (2024)]
.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gabriela Araujo-Pardo (Instituto de Matemáticas\, Universidad Nac
ional Autónoma de Mexico\, Mexico)
DTSTART:20240629T020000Z
DTEND:20240629T033000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/41
DESCRIPTION:Title: On mixed cages\nby Gabriela Araujo-Pardo (Instituto
de Matemáticas\, Universidad Nacional Autónoma de Mexico\, Mexico) as pa
rt of Combinatorics Today Series - ITB\n\n\nAbstract\nA mixed regular grap
h is a graph with both edges and arrows\, where every vertex has the same
number of edges and it has the same number of inside and exit arrows. A cy
cle on a mixed graph is a cycle with edges and arrows with the property th
at all arrows are traversed in the same direction. A mixed cage is a mixed
regular graph with some fixed girth (the smallest length of any cycle) an
d minimum order. These graphs were introduced in 2019 by Araujo-Pardo\, He
rnández\, and Montellano-Ballesteros. From that moment on\, different aut
hors have worked on this topic\, the last published work on this topic was
given by Exoo in 2023. In this talk\, I will give a resume about the stat
e of the art of mixed graphs until this moment. Moreover\, I will talk abo
ut some recent work that I have done with Lydia Mendoza.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Slamin (Universitas Jember\, Indonesia)
DTSTART:20250210T090000Z
DTEND:20250210T103000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/42
DESCRIPTION:Title: The Role of Graph Theory in Machine Learning\nby Sla
min (Universitas Jember\, Indonesia) as part of Combinatorics Today Series
- ITB\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sylwia Cichacz (AGH University in Cracow\, Poland)
DTSTART:20250320T070000Z
DTEND:20250320T083000Z
DTSTAMP:20260404T100117Z
UID:CombinTodaySeries/43
DESCRIPTION:Title: APPLICATION OF ZERO-SUM SETS IN MAGIC-TYPE AND ANTIMAGIC
-TYPE GRAPH LABELING\nby Sylwia Cichacz (AGH University in Cracow\, Po
land) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nLet $(\\G
amma\,+)$ be an Abelian group. A subset $S$ of $\\Gamma$ is called a \\tex
tit{zero-sum subset} if $\\sum_{a\\in S} a=0$. One of the key topics in ze
ro-sum theory is the study of disjoint zero-sum subsets in $\\Gamma$. This
approach was inspired by Steiner triples research and started by Skolem.
\\\\\n\nInterestingly\, certain magic-type and antimagic-type graph labeli
ngs are closely related to disjoint zero-sum subsets in $\\Gamma$. In this
talk\, we will explore some of these connections.\n
LOCATION:https://stable.researchseminars.org/talk/CombinTodaySeries/43/
END:VEVENT
END:VCALENDAR