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BEGIN:VEVENT
SUMMARY:Ben Hollering (North Carolina State University)
DTSTART;VALUE=DATE-TIME:20200409T140000Z
DTEND;VALUE=DATE-TIME:20200409T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/1
DESCRIPTION:Title: I
dentifiability in Phylogenetics using Algebraic Matroids\nby Ben Holle
ring (North Carolina State University) as part of Virtual seminar on algeb
raic matroids and rigidity theory\n\n\nAbstract\nIdentifiability is a cruc
ial property for a statistical model since it implies that distributions i
n the model uniquely determine the parameters that produce them. In phylog
enetics\, the identifiability of the tree parameter is of particular inter
est since it means that phylogenetic models can be used to infer evolution
ary histories from data. Typical strategies for proving identifiability re
sults require Gröbner basis computations which become untenable as the si
ze of the model grows. In this talk I'll give some background on phylogene
tic algebraic geometry and then discuss a new computational strategy for p
roving the identifiability of discrete parameters in algebraic statistical
models that uses algebraic matroids naturally associated to the models. T
his algorithm allows us to avoid computing Gröbner bases and is also para
llelizable.\n
LOCATION:https://researchseminars.org/talk/VSAMRT/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eliana Duarte (Otto-von-Guericke Universität Magdeburg)
DTSTART;VALUE=DATE-TIME:20200423T140000Z
DTEND;VALUE=DATE-TIME:20200423T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/2
DESCRIPTION:Title: R
igidity of 2D and 3D quasicrystal frameworks\nby Eliana Duarte (Otto-v
on-Guericke Universität Magdeburg) as part of Virtual seminar on algebrai
c matroids and rigidity theory\n\n\nAbstract\nDeciding wether a generic 2D
rod-and-pinion framework is rigid can be done by checking that its underl
ying graph satisfies the Laman conditions. For frameworks with a special c
onfiguration such as grids of squares\, there is a simpler way to associat
e a graph to the framework and decide if it is rigid or not. In this 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 results for
cubical frameworks or 3D quasicrystals. Pictures and real time interactive
animations will be present throughout this talk to illustrate important c
oncepts. This talk is based on joint work with George Francis and students
from the Illinois Geometry Lab.\n
LOCATION:https://researchseminars.org/talk/VSAMRT/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jim Cruickshank (NUI Galway)
DTSTART;VALUE=DATE-TIME:20200430T140000Z
DTEND;VALUE=DATE-TIME:20200430T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/3
DESCRIPTION:Title: S
urface graphs\, gain sparsity and some applications in discrete geometry
a>\nby Jim Cruickshank (NUI Galway) as part of Virtual seminar on algebrai
c matroids and rigidity theory\n\n\nAbstract\nA collection of line segment
s in the plane forms a 2-contact system if the segments have pairwise disj
oint interiors and no pair of segments have an endpoint in common. Thomass
en has shown that a graph is the intersection graph of such a 2-contact sy
stem if and only if it is a subgraph of a planar Laman graph. Also Haas\,
Orden\, Rote\, Francisco\, Servatius\, Servatius\, Souvain\, Streinu and W
hiteley have shown that a graph admits a plane embedding as a pointed pseu
dotriangulation if and only if is a planar Laman graph. I will discuss rec
ent work on symmetric versions of these results. In this context the graph
s that arise are naturally embedded in the orbifold associated to the acti
on of the symmetry group\, and the appropriate sparsity conditions are gai
n sparsity conditions. Our main tools are new topological inductive constr
uctions for the appropriate classes of surface graphs. All of the work pre
sented here is joint with Bernd Schulze.\n
LOCATION:https://researchseminars.org/talk/VSAMRT/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tony Nixon (Lancaster)
DTSTART;VALUE=DATE-TIME:20200507T140000Z
DTEND;VALUE=DATE-TIME:20200507T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/4
DESCRIPTION:Title: F
lexible circuits and $d$-dimensional rigidity\nby Tony Nixon (Lancaste
r) as part of Virtual seminar on algebraic matroids and rigidity theory\n\
n\nAbstract\nA framework is a geometric realisation of a graph in Euclidea
n $d$-space. Edges of the graph correspond to bars of the framework and ve
rtices correspond to joints with full rotational freedom. The framework is
rigid if every edge-length-preserving continuous deformation of the verti
ces 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. Characteris
ing which graphs are generically rigid is solved in dimension $1$ and $2$.
However determining an analogous characterisation when $d\\geq 3$ is a lo
ng standing open problem\, and the existence of non-rigid (i.e. flexible)
circuits is a major contributing factor to why this problem is so difficul
t. We begin a study of flexible circuits by characterising the flexible ci
rcuits 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://researchseminars.org/talk/VSAMRT/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Manolis Tsakiri (ShanghaiTech University)
DTSTART;VALUE=DATE-TIME:20200514T140000Z
DTEND;VALUE=DATE-TIME:20200514T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/5
DESCRIPTION:Title: F
initeness of fibers in matrix completion via Plucker coordinates\nby M
anolis Tsakiri (ShanghaiTech University) as part of Virtual seminar on alg
ebraic matroids and rigidity theory\n\n\nAbstract\nWe describe a family of
maximal elements of the algebraic matroid of the determinantal variety of
at most rank-r matrices of size m x n over an infinite field k. For this\
, we formulate matrix completion as a hyperplane sections problem on the G
rassmannian Gr(r\,m) and use a family of local coordinates on Gr(r\,m) ind
uced by linkage matching fields\, as described by Sturmfels & Zelevinsky (
1993). Along the way we prove a conjecture of Rong\, Wang & Xu (2019).\n
LOCATION:https://researchseminars.org/talk/VSAMRT/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jessica Sidman (Mount Holyoke College)
DTSTART;VALUE=DATE-TIME:20200521T140000Z
DTEND;VALUE=DATE-TIME:20200521T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/6
DESCRIPTION:Title: F
rameworks in special position: joints vs edges\nby Jessica Sidman (Mou
nt Holyoke College) as part of Virtual seminar on algebraic matroids and r
igidity theory\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/VSAMRT/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bill Jackson (Queen Mary University of London)
DTSTART;VALUE=DATE-TIME:20200625T140000Z
DTEND;VALUE=DATE-TIME:20200625T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/8
DESCRIPTION:Title: C
ofactor matroids and abstract rigidity\nby Bill Jackson (Queen Mary Un
iversity of London) as part of Virtual seminar on algebraic matroids and r
igidity theory\n\n\nAbstract\nWe verify a conjecture of Walter Whiteley fr
om 1996 that the C^1_2-cofactor matroid is the unique maximal abstract 3-r
igidity matroid. We then use this result to obtain a good chara\n
LOCATION:https://researchseminars.org/talk/VSAMRT/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Patrick Lin (University of Illinois at Urbana-Champaign)
DTSTART;VALUE=DATE-TIME:20200702T140000Z
DTEND;VALUE=DATE-TIME:20200702T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/9
DESCRIPTION:Title: M
axwell-Cremona meets the flat torus\nby Patrick Lin (University of Ill
inois at Urbana-Champaign) as part of Virtual seminar on algebraic matroid
s and rigidity theory\n\n\nAbstract\nWe consider three classes of geodesic
embeddings of graphs on the plane and the Euclidean flat torus: graphs ha
ving a positive equilibrium stress\, reciprocal graphs (for which there is
an orthogonal embedding of the dual graph)\, and weighted Delaunay comple
xes. The classical Maxwell-Cremona correspondence and the well-known corre
spondence between convex hulls and weighted Delaunay triangulations imply
that these three concepts are essentially equivalent for plane graphs. How
ever\, this three-way equivalence does not extend directly to geodesic gra
phs on the torus. Reciprocal and Delaunay graphs are equivalent\, and ever
y reciprocal graph is in positive equilibrium\, but not every positive equ
ilibrium graph is reciprocal. We establish a weaker correspondence: Every
positive equilibrium graph on any flat torus is equivalent to a reciprocal
/Delaunay graph on some flat torus. These results appeared in SoCG '20\n
LOCATION:https://researchseminars.org/talk/VSAMRT/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Irving Bernstein (MIT)
DTSTART;VALUE=DATE-TIME:20200716T140000Z
DTEND;VALUE=DATE-TIME:20200716T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/10
DESCRIPTION:Title:
Generic symmetry-forced infinitesimal rigidity: translations and rotations
\nby Daniel Irving Bernstein (MIT) as part of Virtual seminar on algeb
raic matroids and rigidity theory\n\n\nAbstract\nBar and joint frameworks
appearing in certain applications (particularly crystallography) are often
constrained to have particular symmetries. This motivates the study of sy
mmetric frameworks whose allowable flexes preserve the symmetry. Just as n
on-symmetric frameworks are represented using graphs\, symmetric framework
s are represented using gain graphs\, i.e. directed graphs whose arcs are
labeled by elements of a group. The main result of this talk is a Laman-li
ke characterization of the gain graphs that are generically infinitesimall
y symmetry-forced rigid in the plane when the symmetry group consists of t
ranslations and rotations.\n
LOCATION:https://researchseminars.org/talk/VSAMRT/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ryoshun Oba (University of Tokyo)
DTSTART;VALUE=DATE-TIME:20200723T140000Z
DTEND;VALUE=DATE-TIME:20200723T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/11
DESCRIPTION:Title:
Characterizing the Universal Rigidity of Generic Tensegrities\nby Ryos
hun Oba (University of Tokyo) as part of Virtual seminar on algebraic matr
oids and rigidity theory\n\n\nAbstract\nA tensegrity is a structure made f
rom cables\, struts and stiff bars. A d-dimensional tensegirty is universa
lly rigid if it is rigid in any dimension d′ with d′≥d. The celebrat
ed super stability condition due to Connelly gives a sufficient condition
for a tensegrity to be universally rigid. Gortler and Thurston showed that
super stability characterizes universal rigidity when the point configura
tion is generic and every member is a stiff bar. We extend this result in
two directions. We first show that a generic universally rigid tensegrity
is super stable. We then extend it to tensegrities with point group symmet
ry\, and show that this characterization still holds as long as a tensegri
ty is generic modulo symmetry. Our strategy is based on the block-diagonal
ization technique for symmetric semidefinite programming problems\, and ou
r proof relies on the theory of real irreducible representation of finite
groups.\n
LOCATION:https://researchseminars.org/talk/VSAMRT/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sean Dewar (Johann Radon Institute of Computational and Applied Ma
thematics)
DTSTART;VALUE=DATE-TIME:20200910T140000Z
DTEND;VALUE=DATE-TIME:20200910T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/12
DESCRIPTION:Title:
Which graphs are rigid in lp spaces?\nby Sean Dewar (Johann Radon Inst
itute of Computational and Applied Mathematics) as part of Virtual seminar
on algebraic matroids and rigidity theory\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/VSAMRT/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nikki Meshkat (Santa Clara University)
DTSTART;VALUE=DATE-TIME:20200917T150000Z
DTEND;VALUE=DATE-TIME:20200917T160000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/13
DESCRIPTION:Title:
Identifiability and observability of biological models using algebraic mat
roids\nby Nikki Meshkat (Santa Clara University) as part of Virtual se
minar on algebraic matroids and rigidity theory\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/VSAMRT/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tony Nixon (Lancaster University)
DTSTART;VALUE=DATE-TIME:20200924T140000Z
DTEND;VALUE=DATE-TIME:20200924T150000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
UID:VSAMRT/14
DESCRIPTION:Title:
Rigidity of linearly constrained frameworks in d-dimensions\nby Tony N
ixon (Lancaster University) as part of Virtual seminar on algebraic matroi
ds and rigidity theory\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/VSAMRT/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Elizabeth Gross (University of Hawai'i at Mānoa)
DTSTART;VALUE=DATE-TIME:20201022T190000Z
DTEND;VALUE=DATE-TIME:20201022T200000Z
DTSTAMP;VALUE=DATE-TIME:20240328T124751Z
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://researchseminars.org/talk/VSAMRT/15/
END:VEVENT
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