BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Ben Hollering (North Carolina State University) DTSTART:20200409T140000Z DTEND:20200409T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/1 DESCRIPTION:Title: Identifiability in Phylogenetics using Algebraic Matroids\nby Be n Hollering (North Carolina State University) as part of Virtual seminar o n algebraic matroids and rigidity theory\n\n\nAbstract\nIdentifiability is a crucial property for a statistical model since it implies that distribu tions in the model uniquely determine the parameters that produce them. In phylogenetics\, the identifiability of the tree parameter is of particula r interest since it means that phylogenetic models can be used to infer ev olutionary histories from data. Typical strategies for proving identifiabi lity results require Gröbner basis computations which become untenable as the size of the model grows. In this talk I'll give some background on ph ylogenetic algebraic geometry and then discuss a new computational strateg y for proving the identifiability of discrete parameters in algebraic stat istical models that uses algebraic matroids naturally associated to the mo dels. This algorithm allows us to avoid computing Gröbner bases and is al so parallelizable.\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Eliana Duarte (Otto-von-Guericke Universität Magdeburg) DTSTART:20200423T140000Z DTEND:20200423T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/2 DESCRIPTION:Title: Rigidity of 2D and 3D quasicrystal frameworks\nby Eliana Duarte (Otto-von-Guericke Universität Magdeburg) as part of Virtual seminar on a lgebraic matroids and rigidity theory\n\n\nAbstract\nDeciding wether a gen eric 2D rod-and-pinion framework is rigid can be done by checking that its underlying graph satisfies the Laman conditions. For frameworks with a sp ecial configuration such as grids of squares\, there is a simpler way to a ssociate a graph to the framework and decide if it is rigid or not. In thi s talk I will consider frameworks that come from Penrose tilings and show that we can decide the rigidity of these frameworks as we do for grids of squares. There is no generalization of Laman conditions for rigidity of 3D graphs but perhaps we can prove (conjecture) a generalization of 2D resul ts for cubical frameworks or 3D quasicrystals. Pictures and real time inte ractive animations will be present throughout this talk to illustrate impo rtant concepts. This talk is based on joint work with George Francis and s tudents from the Illinois Geometry Lab.\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Jim Cruickshank (NUI Galway) DTSTART:20200430T140000Z DTEND:20200430T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/3 DESCRIPTION:Title: Surface graphs\, gain sparsity and some applications in discrete geo metry\nby Jim Cruickshank (NUI Galway) as part of Virtual seminar on a lgebraic matroids and rigidity theory\n\n\nAbstract\nA collection of line segments in the plane forms a 2-contact system if the segments have pairwi se disjoint interiors and no pair of segments have an endpoint in common. Thomassen has shown that a graph is the intersection graph of such a 2-con tact system if and only if it is a subgraph of a planar Laman graph. Also Haas\, Orden\, Rote\, Francisco\, Servatius\, Servatius\, Souvain\, Strein u and Whiteley have shown that a graph admits a plane embedding as a point ed pseudotriangulation if and only if is a planar Laman graph. I will disc uss recent work on symmetric versions of these results. In this context th e graphs that arise are naturally embedded in the orbifold associated to t he action of the symmetry group\, and the appropriate sparsity conditions are gain sparsity conditions. Our main tools are new topological inductive constructions for the appropriate classes of surface graphs. All of the w ork presented here is joint with Bernd Schulze.\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Tony Nixon (Lancaster) DTSTART:20200507T140000Z DTEND:20200507T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/4 DESCRIPTION:Title: Flexible circuits and $d$-dimensional rigidity\nby Tony Nixon (L ancaster) as part of Virtual seminar on algebraic matroids and rigidity th eory\n\n\nAbstract\nA framework is a geometric realisation of a graph in E uclidean $d$-space. Edges of the graph correspond to bars of the framework and vertices correspond to joints with full rotational freedom. The frame work is rigid if every edge-length-preserving continuous deformation of th e vertices arises from isometries of $d$-space. Generically\, rigidity is a rank condition on an associated rigidity matrix and hence is a property of the graph which can be described by the corresponding row matroid. Char acterising which graphs are generically rigid is solved in dimension $1$ a nd $2$. However determining an analogous characterisation when $d\\geq 3$ is a long standing open problem\, and the existence of non-rigid (i.e. fle xible) circuits is a major contributing factor to why this problem is so d ifficult. We begin a study of flexible circuits by characterising the flex ible circuits in $d$-dimensions which have at most $d+6$ vertices. This is joint work with Georg Grasegger\, Hakan Guler and Bill Jackson.\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Manolis Tsakiri (ShanghaiTech University) DTSTART:20200514T140000Z DTEND:20200514T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/5 DESCRIPTION:Title: Finiteness of fibers in matrix completion via Plucker coordinates\nby Manolis Tsakiri (ShanghaiTech University) as part of Virtual seminar on algebraic matroids and rigidity theory\n\n\nAbstract\nWe describe a fa mily of maximal elements of the algebraic matroid of the determinantal var iety of at most rank-r matrices of size m x n over an infinite field k. Fo r this\, we formulate matrix completion as a hyperplane sections problem o n the Grassmannian Gr(r\,m) and use a family of local coordinates on Gr(r\ ,m) induced by linkage matching fields\, as described by Sturmfels & Zelev insky (1993). Along the way we prove a conjecture of Rong\, Wang & Xu (201 9).\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Jessica Sidman (Mount Holyoke College) DTSTART:20200521T140000Z DTEND:20200521T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/6 DESCRIPTION:Title: Frameworks in special position: joints vs edges\nby Jessica Sidm an (Mount Holyoke College) as part of Virtual seminar on algebraic matroid s and rigidity theory\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Bill Jackson (Queen Mary University of London) DTSTART:20200625T140000Z DTEND:20200625T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/8 DESCRIPTION:Title: Cofactor matroids and abstract rigidity\nby Bill Jackson (Queen Mary University of London) as part of Virtual seminar on algebraic matroid s and rigidity theory\n\n\nAbstract\nWe verify a conjecture of Walter Whit eley from 1996 that the C^1_2-cofactor matroid is the unique maximal abstr act 3-rigidity matroid. We then use this result to obtain a good chara\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Patrick Lin (University of Illinois at Urbana-Champaign) DTSTART:20200702T140000Z DTEND:20200702T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/9 DESCRIPTION:Title: Maxwell-Cremona meets the flat torus\nby Patrick Lin (University of Illinois at Urbana-Champaign) as part of Virtual seminar on algebraic matroids and rigidity theory\n\n\nAbstract\nWe consider three classes of g eodesic embeddings of graphs on the plane and the Euclidean flat torus: gr aphs having a positive equilibrium stress\, reciprocal graphs (for which t here is an orthogonal embedding of the dual graph)\, and weighted Delaunay complexes. The classical Maxwell-Cremona correspondence and the well-know n correspondence between convex hulls and weighted Delaunay triangulations imply that these three concepts are essentially equivalent for plane grap hs. However\, this three-way equivalence does not extend directly to geode sic graphs on the torus. Reciprocal and Delaunay graphs are equivalent\, a nd every reciprocal graph is in positive equilibrium\, but not every posit ive equilibrium graph is reciprocal. We establish a weaker correspondence: Every positive equilibrium graph on any flat torus is equivalent to a rec iprocal/Delaunay graph on some flat torus. These results appeared in SoCG '20\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Irving Bernstein (MIT) DTSTART:20200716T140000Z DTEND:20200716T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/10 DESCRIPTION:Title: Generic symmetry-forced infinitesimal rigidity: translations and ro tations\nby Daniel Irving Bernstein (MIT) as part of Virtual seminar o n algebraic matroids and rigidity theory\n\n\nAbstract\nBar and joint fram eworks appearing in certain applications (particularly crystallography) ar e often constrained to have particular symmetries. This motivates the stud y of symmetric frameworks whose allowable flexes preserve the symmetry. Ju st as non-symmetric frameworks are represented using graphs\, symmetric fr ameworks are represented using gain graphs\, i.e. directed graphs whose ar cs are labeled by elements of a group. The main result of this talk is a L aman-like characterization of the gain graphs that are generically infinit esimally symmetry-forced rigid in the plane when the symmetry group consis ts of translations and rotations.\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Ryoshun Oba (University of Tokyo) DTSTART:20200723T140000Z DTEND:20200723T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/11 DESCRIPTION:Title: Characterizing the Universal Rigidity of Generic Tensegrities\n by Ryoshun Oba (University of Tokyo) as part of Virtual seminar on algebra ic matroids and rigidity theory\n\n\nAbstract\nA tensegrity is a structure made from cables\, struts and stiff bars. A d-dimensional tensegirty is u niversally rigid if it is rigid in any dimension d′ with d′≥d. The c elebrated super stability condition due to Connelly gives a sufficient con dition for a tensegrity to be universally rigid. Gortler and Thurston show ed that super stability characterizes universal rigidity when the point co nfiguration is generic and every member is a stiff bar. We extend this res ult in two directions. We first show that a generic universally rigid tens egrity is super stable. We then extend it to tensegrities with point group symmetry\, and show that this characterization still holds as long as a t ensegrity is generic modulo symmetry. Our strategy is based on the block-d iagonalization technique for symmetric semidefinite programming problems\, and our proof relies on the theory of real irreducible representation of finite groups.\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Sean Dewar (Johann Radon Institute of Computational and Applied Ma thematics) DTSTART:20200910T140000Z DTEND:20200910T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/12 DESCRIPTION:Title: Which graphs are rigid in lp spaces?\nby Sean Dewar (Johann Rad on Institute of Computational and Applied Mathematics) as part of Virtual seminar on algebraic matroids and rigidity theory\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Nikki Meshkat (Santa Clara University) DTSTART:20200917T150000Z DTEND:20200917T160000Z DTSTAMP:20260404T110831Z UID:VSAMRT/13 DESCRIPTION:Title: Identifiability and observability of biological models using algebr aic matroids\nby Nikki Meshkat (Santa Clara University) as part of Vir tual seminar on algebraic matroids and rigidity theory\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Tony Nixon (Lancaster University) DTSTART:20200924T140000Z DTEND:20200924T150000Z DTSTAMP:20260404T110831Z UID:VSAMRT/14 DESCRIPTION:Title: Rigidity of linearly constrained frameworks in d-dimensions\nby Tony Nixon (Lancaster University) as part of Virtual seminar on algebraic matroids and rigidity theory\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Elizabeth Gross (University of Hawai'i at Mānoa) DTSTART:20201022T190000Z DTEND:20201022T200000Z DTSTAMP:20260404T110831Z UID:VSAMRT/15 DESCRIPTION:by Elizabeth Gross (University of Hawai'i at Mānoa) as part o f Virtual seminar on algebraic matroids and rigidity theory\n\nAbstract: T BA\n LOCATION:https://stable.researchseminars.org/talk/VSAMRT/15/ END:VEVENT END:VCALENDAR