To add a seminar or a talk, please email Aram directly. If you want to see math seminars of all disciplines, you can try the following website.

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The following is a list of online conferences that are happening during the pandemic! If you have a conference you'd like to add, feel free to email me. 😃

All times are denoted in your local computer time. Roughly the next two weeks are shown.

It is currently: **Wed 27 Jan 2021 08:04 UTC**

Last updated: Mon 25 Jan 2021 17:47 UTC

Green - Talk is currently happening.

Yellow - Talk is coming up within the hour.

Red - Talk is in under 10 minutes.

**Zoom links can be found on seminar/conference websites** (They have been removed for security reasons)

Speaker | Title | Date & Time | Duration | Abstract | Seminar |
---|---|---|---|---|---|

Asilata Bapat | TBA | Wed 27 Jan 2021 10:00 UTC | 60 minutes | No abstract available | 20 |

Alex McDonough, Brown University | A Higher-Dimensional Sandpile Map (pre-talk) | Wed 27 Jan 2021 23:30 UTC | 30 minutes | Show | 33 |

Alex McDonough, Brown University | A Higher-Dimensional Sandpile Map | Thu 28 Jan 2021 00:10 UTC | 50 minutes | Show | 33 |

Aram Dermenjian, York University | Sign Variations and Descents | Thu 28 Jan 2021 17:30 UTC | 50 minutes | Show | 24 |

Olya Mandelshtam | The multispecies TAZRP and modified Macdonald polynomials | Thu 28 Jan 2021 18:00 UTC | 50 minutes | No abstract available | 26 |

Victor S. Miller, Center for Communications Research, Princeton | Counting Matrices that are Squares | Thu 28 Jan 2021 22:00 UTC | 48 minutes | Show | 21 |

Gregory Bodwin (University of Michigan) | On the structure of unique shortest paths in graphs | Fri 29 Jan 2021 20:00 UTC | 60 minutes | Show | 30 |

Speaker | Title | Date & Time | Duration | Abstract | Seminar |
---|---|---|---|---|---|

Sjanne Zeijlemaker | TBA | Mon 01 Feb 2021 16:30 UTC | Check Seminar Page | No abstract available | 34 |

Andrés Vindas Meléndez (University of Kentucky) | TBA | Mon 01 Feb 2021 20:00 UTC | 60 minutes | No abstract available | 38 |

Meike Hatzel | TBA | Mon 01 Feb 2021 20:00 UTC | Check Seminar Page | No abstract available | 10 |

Christopher Ryba UC Berkeley | Stable characters from permutation patterns | Mon 01 Feb 2021 20:10 UTC | 50 minutes | Show | 23 |

Lisa Sauermann (IAS) | On the extension complexity of low-dimensional polytopes | Tue 02 Feb 2021 14:00 UTC | Check Seminar Page | Show | 18 |

Nathanaël Berestycki (Vienna) | Free boundary dimers: random walk representation and scaling limit | Tue 02 Feb 2021 15:30 UTC | Check Seminar Page | Show | 18 |

Rosa Winter (MPI MIS, Leipzig) | Linear spaces of symmetric matrices with non-maximal maximum likelihood degree | Tue 02 Feb 2021 16:00 UTC | 45 minutes | Show | 11 |

Leonid Chekhov (Steklov Mathematical Institute) | Darboux coordinates for symplectic groupoid and cluster algebras | Tue 02 Feb 2021 16:00 UTC | Check Seminar Page | Show | 17 |

Juliette Bruce (University of California, Berkeley) | The top weight cohomology of $A_g$ | Tue 02 Feb 2021 16:45 UTC | 45 minutes | Show | 11 |

Inna Entova-Aizenbud | TBA | Wed 03 Feb 2021 16:00 UTC | 60 minutes | No abstract available | 20 |

Foster Tom (UC Berkeley) | A combinatorial Schur expansion of triangle-free horizontal-strip LLT polynomials | Wed 03 Feb 2021 18:00 UTC | 60 minutes | Show | 16 |

Farid Aliniaeifard, The University of British Columbia | A categorification of the Malvenuto-Reutenauer algebra via a tower of groups (pre-talk) | Wed 03 Feb 2021 23:30 UTC | 30 minutes | Show | 33 |

Farid Aliniaeifard, The University of British Columbia | A categorification of the Malvenuto-Reutenauer algebra via a tower of groups | Thu 04 Feb 2021 00:10 UTC | 50 minutes | Show | 33 |

Andreas Thom (TU Dresden) | TBA | Thu 04 Feb 2021 15:10 UTC | 50 minutes | No abstract available | 1 |

Melissa Zhang, U of Georgia | TBA | Thu 04 Feb 2021 17:30 UTC | 50 minutes | No abstract available | 24 |

Jessica Striker | TBA | Thu 04 Feb 2021 18:00 UTC | 50 minutes | No abstract available | 26 |

Ron Adin, Bar Ilan University, Israel | Cyclic permutations, shuffles, and quasi-symmetric functions | Thu 04 Feb 2021 22:00 UTC | 48 minutes | Show | 21 |

Eduardo Sáenz de Cabezón (Universidad de La Rioja) | Polarización y depolarización de ideales monomiales con una mirada hacia la fiabilidad de sistemas industriales | Fri 05 Feb 2021 17:00 UTC | 60 minutes | Show | 15 |

Roi Docampo (University Oklahoma) | TBA | Fri 05 Feb 2021 21:30 UTC | 60 minutes | No abstract available | 13 |

Rob Davis (Colgate University) | TBA | Fri 05 Feb 2021 21:35 UTC | 50 minutes | No abstract available | 31 |

Speaker | Title | Date & Time | Duration | Abstract | Seminar |
---|---|---|---|---|---|

Juliette Bruce (UC Berkeley and MSRI) | TBA | Mon 08 Feb 2021 16:00 UTC | 50 minutes | No abstract available | 14 |

Thomas McConville (Kennesaw State University) | TBA | Mon 08 Feb 2021 19:00 UTC | 60 minutes | No abstract available | 28 |

Matteo Mucciconi (Tokyo Institute of Technology) | TBA | Mon 08 Feb 2021 20:00 UTC | 60 minutes | No abstract available | 38 |

Camille Combe Universite de Paris | TBA | Mon 08 Feb 2021 20:10 UTC | 50 minutes | No abstract available | 23 |

David Wood | TBA | Mon 08 Feb 2021 22:00 UTC | Check Seminar Page | No abstract available | 10 |

Daniel Nakano | TBA | Wed 10 Feb 2021 16:00 UTC | 60 minutes | No abstract available | 20 |

Sophie Rehberg (FU Berlin) | Combinatorial reciprocity theorems for generalized permutahedra, hypergraphs, and pruned inside-out polytopes | Wed 10 Feb 2021 18:00 UTC | 60 minutes | Show | 16 |

Patricia Hersh (U Oregon) | TBA | Wed 10 Feb 2021 23:00 UTC | 60 minutes | No abstract available | 32 |

Dominic Verdon (University of Bristol) | TBA | Thu 11 Feb 2021 15:10 UTC | 50 minutes | No abstract available | 1 |

Sophie Spirkl (Waterloo) | TBA | Thu 11 Feb 2021 20:00 UTC | Check Seminar Page | No abstract available | 19 |

Colin Defant, Princeton University | Cumulants and Stack-Sorting | Thu 11 Feb 2021 22:00 UTC | 48 minutes | Show | 21 |

Sunita Chepuri (University of Michigan) | TBA | Fri 12 Feb 2021 20:00 UTC | 60 minutes | No abstract available | 30 |

Angelica Babei | TBA | Fri 12 Feb 2021 21:30 UTC | 60 minutes | No abstract available | 13 |

Ruriko Yoshida (Naval Postgraduate School) | TBA | Mon 15 Feb 2021 19:00 UTC | 60 minutes | No abstract available | 28 |

Hyun Kyu Kim (Ewha Womans University) | SL3-laminations as bases for PGL3 cluster varieties for surfaces | Tue 16 Feb 2021 16:00 UTC | Check Seminar Page | Show | 17 |

Luca Sodomaco (Aalto University) | TBA | Tue 16 Feb 2021 16:00 UTC | 45 minutes | No abstract available | 11 |

Elizabeth Gross (University of Hawai`i at Mānoa) | TBA | Tue 16 Feb 2021 16:45 UTC | 45 minutes | No abstract available | 11 |

Amzi Jeffs (University of Washington) | Convex Codes: Realizations, Minors, and Embedding Dimensions | Wed 17 Feb 2021 18:00 UTC | 60 minutes | Show | 16 |

Michael Krivelevich (Tel Aviv) | TBA | Thu 18 Feb 2021 20:00 UTC | Check Seminar Page | No abstract available | 19 |

Jaqueline Godoy Mesquita (Universidade de Brasília) | TBA | Fri 19 Feb 2021 17:00 UTC | 60 minutes | No abstract available | 15 |

Rob Davis (Colgate University) | TBA | Fri 19 Feb 2021 21:30 UTC | 60 minutes | No abstract available | 13 |

Seminar Number | Name | Institution | Website |
---|---|---|---|

1 | Geometry, Algebra, Mathematical Physics and Topology Research Group | Cardiff Univesity | Seminar Website |

2 | Algorithms, Combinatorics and Optimization Seminar | Carnegie Mellon University | Seminar Website |

3 | New York Combinatorics Seminar | City University of New York | Seminar Website |

4 | Rocky Mountain Algebraic Combinatorics Seminar | Colorado State University | Seminar Website |

5 | Algebraic Combinatorics Seminar | Institute of Mathematical Sciences | Seminar Website |

6 | LIPN Seminar | Laboratoire d'Informatique de Paris Nord | Seminar Website |

7 | Los Angeles Combinatorics and Complexity Seminar | Los Angeles | Seminar Website |

8 | MIT-Harvard-MSR Combinatorics Seminar | MIT, Harvard, MSR | Seminar Website |

9 | Virtual seminar on algebraic matroids and rigidity theory | Massachussetts Institute of Technology | Seminar Website |

10 | Online Matroid Theory Seminar | Matroid Union | Seminar Website |

11 | Nonlinear Algebra Seminar Online | Max-Planck-Instut für Mathematik (MPI) | Seminar Website |

12 | Virtual Combinatorics Colloquium | Northeast Combinatorics Network | Seminar Website |

13 | Algebra and Representation Theory Seminar | Oklahoma University | Seminar Website |

14 | Algebra, Geometry and Combinatorics | Online | Seminar Website |

15 | Cibercoloquio Latinoamericano de Mathemáticas | Online | Seminar Website |

16 | Graduate Online Combinatorics Colloquium | Online | Seminar Website |

17 | Online Cluster Algebra Seminar | Online | Seminar Website |

18 | Oxford Discrete mathematics and probability seminar | Oxford University | Seminar Website |

19 | Princeton Discrete Mathematics Seminar | Princeton University | Seminar Website |

20 | The RepNet Virtual Seminar | RepNet | Seminar Website |

21 | Rutgers Experimental Mathematics Seminar | Rutgers University | Seminar Website |

22 | Workshop on combinatorics, discrete geometry and algorithms | St. Petersburg State University | Seminar Website |

23 | Combinatorics Seminar | UC Berkeley | Seminar Website |

24 | Algebra and Discrete Mathematics Seminar | UC Davis | Seminar Website |

25 | UCLA Combinatorics Seminar | UCLA | Seminar Website |

26 | Algebraic (and enumerative) combinatorics seminar | UWaterloo | Seminar Website |

27 | Lie Theory seminar | University of Colorado, Boulder | Seminar Website |

28 | Discrete CATS Seminar | University of Kentucky | Seminar Website |

29 | Discrete Math Seminar | University of Massachusetts Amherst | Seminar Website |

30 | Combinatorics Seminar | University of Michigan | Seminar Website |

31 | Combinatorics Seminar | University of Minnesota | Seminar Website |

32 | USC Combinatorics Seminar | University of Southern California | Seminar Website |

33 | Combinatorics and Geometry Seminar | University of Washington | Seminar Website |

34 | Algebraic Graph Theory | University of Waterloo | Seminar Website |

35 | Séminaire de combinatoire et d'informatique mathématique du LaCIM | Université du Québec à Montréal | Seminar Website |

36 | WUSTL Combinatorics Seminar | Washington University in St. Louis | Seminar Website |

37 | WinCom Virtual Colloquium | Women in Combinatorics | Seminar Website |

38 | Applied Algebra Seminar | York University | Seminar Website |

Traditionally, the sandpile group is defined on a graph and the Matrix-Tree Theorem says that this group's size is equal to the number of spanning trees. An extension of the Matrix-Tree Theorem gives a relationship between the sandpile group and bases of an orientable arithmetic matroid. I provide a family of combinatorially meaningful maps between these two sets. This generalizes a bijection given by Backman, Baker, and Yuen and extends work by Duval, Klivans, and Martin. I will not assume any background beyond undergraduate linear algebra.

CloseTraditionally, the sandpile group is defined on a graph and the Matrix-Tree Theorem says that this group's size is equal to the number of spanning trees. An extension of the Matrix-Tree Theorem gives a relationship between the sandpile group and bases of an orientable arithmetic matroid. I provide a family of combinatorially meaningful maps between these two sets. This generalizes a bijection given by Backman, Baker, and Yuen and extends work by Duval, Klivans, and Martin. I will not assume any background beyond undergraduate linear algebra.

CloseIn this talk we consider a poset structure on projective sign vectors. We show that the order complex of this poset is partitionable and give an interpretation of the h-vector using type B descents of the type D Coxeter group.

CloseOn the math-fun mailing list (7 May 2013), Neil Sloane asked to calculate the number of n times n matrices with entries in {0,1} which are squares of other such matrices. In this paper we analyze the case that the arithmetic is in GF(2) We follow the dictum of Wilf (in the paper ``What is an answer?'') to derive a ``effective'' algorithm to count such matrices in much less time than it takes to enumerate them. The algorithm which we use involves the analysis of conjugacy classes of matrices. The restricted integer partitions which arise are counted by the coefficients of one of Ramanujan's mock Theta functions, which we found thanks to Sloane's OEIS (Online Encyclopedia of Integer Sequences).

CloseLet P be a system of unique shortest paths through a graph with real edge weights. A well-known fact is that P must be "consistent," meaning that no two of these paths can intersect each other, split apart, and then intersect again later. But is that all the guaranteed structure? Can any consistent path system be realized as unique shortest paths in some graph? Or are there more forbidden combinatorial intersection patterns that can be found?

In this talk, we will complete the list of forbidden intersection patterns for systems of unique shortest paths, characterizing the set of unique shortest path systems via forbidden patterns. We will then say a little about some connections between graph metrics and topology that enable our characterization theorem.

For a fixed permutation σ∈Sk, let Nσ denote the function which counts occurrences of σ as a pattern in permutations from Sn. We study the expected value (and d-th moments) of Nσ on conjugacy classes of Sn and prove that the irreducible character support of these class functions stabilizes as n grows. This says that there is a single polynomial in the variables n,m1,…,mdk which computes these moments on any conjugacy class (of cycle type 1^m1,2^m2,⋯) of any symmetric group. Our proof is, to our knowledge, the first application of partition algebras to the study of permutation patterns. This is joint work with Christian Gaetz.

CloseIt is sometimes possible to represent a complicated polytope as a projection of a much simpler polytope. To quantify this phenomenon, the extension complexity of a polytope P is defined to be the minimum number of facets in a (possibly higher-dimensional) polytope from which P can be obtained as a (linear) projection. In this talk, we discuss some results on the extension complexity of random d-dimensional polytopes (obtained as convex hulls of random points on either on the unit sphere or in the unit ball), and on the extension complexity of polygons with all vertices on a common circle. Joint work with Matthew Kwan and Yufei Zhao.

CloseThe dimer model, a classical model of statistical mechanics, is the uniform distribution on perfect matchings of a graph. In two dimensions, one can define an associated height function which turns the model into a random surface (with specified boundary conditions). In the 1960s, Kasteleyn and Temperley/Fisher found an exact "solution" to the model, computing the correlations in terms of a matrix called the Kasteleyn matrix. This exact solvability was the starting point for the breakthrough work of Kenyon (2000) who proved that the centred height function converges to the Dirichlet (or zero boundary conditions) Gaussian free field. This was the first proof of conformal invariance in statistical mechanics.

In this talk, I will focus on a natural modification of the model where one allows the vertices on the boundary of the graph to remain unmatched: this is the so-called monomer-dimer model, or dimer model with free boundary conditions. The main result that we obtain is that the scaling limit of the height function of the monomer-dimer model in the upper half-plane is the Neumann (or free boundary conditions) Gaussian free field. Key to this result is a somewhat miraculous random walk representation for the inverse Kasteleyn matrix, which I hope to discuss.

Joint work with Marcin Lis (Vienna) and Wei Qian (Paris).

Maximum likelihood estimation is an optimization problem used to fit empirical data to a statistical model. The number of complex critical points to this problem when using generic data is the maximum likelihood degree (ML-degree) of the model. The concentration matrices of certain models form a spectrahedron in the space of symmetric matrices, defined by the intersection of a linear subspace $\mathcal{L}$ with the cone of positive definite matrices. It is known what the ML-degree should be for such models when $\mathcal{L}$ is generic. In this talk I will describe the ’non-generic’ linear subspaces, that is, those for which the corresponding model has ML-degree lower than expected. More specifically, for fixed $k$ and $n$, I will describe the geometry of the Zariski closure in the Grassmanian $G$ $(k,(\substack{n+1\2}))$ of the set of $k$-dimensional linear subspaces of symmetric $n \times n$ matrices that are ’non-generic’ in this sense. I will show that this closed set coincides with the set of linear subspaces of symmetric matrices for which strong duality in semi-definite programming fails. This is joint work with Yuhan Jiang and Kathlén Kohn.

CloseThe talk is based on Arxiv:2003:07499, joint work with Misha Shapiro. We use Fock--Goncharov higher Teichmüller space variables to derive Darboux coordinate representation for entries of general symplectic leaves of the $mathcal A_n$ groupoid of upper-triangular matrices and, in a more general setting, of higher-dimensional symplectic leaves for algebras governed by the quantum reflection equation with the trigonometric $R$-matrix. This result can be generalized to any planar directed network on disc with separated sinks and sources. For the groupoid of upper-triangular matrices, we represent braid-group transformations via sequences of cluster mutations in the special $mathbb A_n$-quiver. We prove the groupoid relations for quantum transport matrices and, as a byproduct, obtain quantum commutation relations having the Goldman bracket as their semiclassical limit. Time permitting, I will also describe a generalization of this construction to affine Lie-Poisson algebras and to quantum loop algebras (Arxiv:2012:10982).

CloseI will discuss recent work calculating the top weight cohomology of the moduli space $A_g$ of principally polarized abelian varieties of dimension g for small values of g. The key idea is that this piece of cohomology is encoded combinatorially via the relationship between the boundary complex of a compactification of $A_g$ and the moduli space of tropical abelian varieties. This is joint work with Madeline Brandt, Melody Chan, Margarida Melo, Gwyneth Moreland, and Corey Wolfe.

CloseIn recent years, Alexandersson and others proved combinatorial formulas for the Schur function expansion of the horizontal-strip LLT polynomial $G_{\bm\lambda}(\bm x;q)$ in some special cases. We associate a weighted graph $\Pi$ to $\bm\lambda$ and we use it to express a linear relation among LLT polynomials. We apply this relation to prove an explicit combinatorial Schur-positive expansion of $G_{\bm\lambda}(\bm x;q)$ whenever $\Pi$ is triangle-free. We also prove that the largest power of $q$ in the LLT polynomial is the total edge weight of our graph.

CloseThere is a long tradition of categorifying combinatorial Hopf algebras by the modules of a tower of algebras (or even better via the representation theory of a tower of groups). From the point of view of combinatorics, such a categorification supplies canonical bases, inner products, and a natural avenue to prove positivity results. Recent ideas in supercharacter theory have made fashioning the representation theory of a tower of groups into a Hopf structure more tractable. As a demonstration, this talk reports on the results of the following challenge: (1) Pick a well-known combinatorial Hopf algebra, (2) Find a way to categorify the structure via a tower of groups. In this case, we show how to find the Malvenuto Reutenauer Hopf algebra in the representation theory of a tower of elementary abelian p-groups (with Nat Thiem).

CloseThere is a long tradition of categorifying combinatorial Hopf algebras by the modules of a tower of algebras (or even better via the representation theory of a tower of groups). From the point of view of combinatorics, such a categorification supplies canonical bases, inner products, and a natural avenue to prove positivity results. Recent ideas in supercharacter theory have made fashioning the representation theory of a tower of groups into a Hopf structure more tractable. As a demonstration, this talk reports on the results of the following challenge: (1) Pick a well-known combinatorial Hopf algebra, (2) Find a way to categorify the structure via a tower of groups. In this case, we show how to find the Malvenuto Reutenauer Hopf algebra in the representation theory of a tower of elementary abelian p-groups (with Nat Thiem).

CloseRichard Stanley proved that the distribution of descent number over all the shuffles of two permutations depends only on the descent numbers of the permutations.

We present an explicit cyclic analogue of this result. The tools used for the proof include a new cyclic counterpart of Gessels quasi-symmetric functions, an unusual ring homomorphism, and a mysterious binomial identity with an interesting history.

Based on joint work with Ira Gessel, Vic Reiner, and Yuval Roichman.

La polarización de ideales monomiales establece una relación entre ideales monomiales generales e ideales monomiales libres de cuadrados. Esta relación mantiene muchas propiedades e invariantes importantes y ha sido estudiada con intensidad. Menos estudiada ha sido la operación inversa, la depolarización. En esta charla abordaremos ese estudio y lo aplicaremos a la fiabilidad algebraica (el estudio de sistemas coherentes mediante técnicas de álgebra conmutativa).

CloseGeneralized permutahedra are a class of polytopes with many interesting combinatorial subclasses. We introduce pruned inside-out polytopes, a generalization of concepts introduced by Beck-Zaslavsky (2006),which have many applications such as recovering the famous reciprocity result for graph colorings by Stanley. We study the integer point count of pruned inside-out polytopes by applying classical Ehrhart polynomials and Ehrhart-Macdonald reciprocity. This yields a geometric perspective on and a generalization of a combinatorial reciprocity theorem for generalized permutahedra by Aguiar-Ardila (2017) and Billera-Jia-Reiner (2009). Applying this reciprocity theorem to hypergraphic polytopes allows us to give an arguably simpler proof of a recent combinatorial reciprocity theorem for hypergraph colorings by Aval-Karaboghossian-Tanasa (2020). Our proof relies, aside from the reciprocity for generalized permutahedra, only on elementary geometric and combinatorial properties of hypergraphs and their associated polytopes.

CloseCumulant sequences are numerical sequences that play a fundamental role in noncommutative probability theory. West's stack-sorting map is a combinatorially-defined operator that acts on permutations. In this talk, we will discuss how cumulants and stack-sorting, two topics from very disparate worlds, are actually very closely related. This unexpected connection allows us to use tools from noncommutative probability theory to prove difficult, surprising, and (occasionally) weird facts about the stack-sorting map. We will explore several applications of this method.

CloseIn this talk, I describe a solution to Fock-Goncharov's duality conjecture for cluster varieties associated to certain moduli spaces of G-local systems on a punctured surface S with boundary data, when G is a group of type A2, namely SL3 and PGL3. I will introduce the notion of SL3-laminations, based on Kuperberg's A2-type webs, and explain how some subclass of SL3-laminations provide a model for tropical integer points of the cluster A moduli space A_{SL3, S}. I will describe the duality map which assigns to each such SL3-lamination a regular function on the cluster X moduli space X_{PGL3,S}. I will sketch proofs of the properties of this map, and also mention a quantization by the SL3 quantum trace map.

CloseHow can we arrange convex sets in Euclidean space? Versions of this question arise in many combinatorial and geometric contexts: hyperplane arrangements, the study of polytopes and simplicial complexes, optimization, and more. In this talk we'll look at convex codes, a relatively recent topic of research that seeks to answer this question very generally. We'll discuss an abstract framework for studying convex codes, some geometric theorems that help us understand them, and see how they differ fundamentally from more classical ideas like nerve complexes.

CloseThe study of convex neural codes seeks to classify the intersection and covering patterns of convex sets in Euclidean space. A specific instance of this is to classify "convex union representable" (CUR) complexes: the simplicial complexes that arise as the nerve of a collection of convex sets whose union is convex. In 2018 Chen, Frick, and Shiu showed that CUR complexes are always collapsible, and asked if the converse holds: is every collapsible complex also CUR? We will provide a negative answer to this question, and more generally describe the combinatorial consequences arising from the geometric representations of CUR complexes. This talk is based on joint work with Isabella Novik.

Close