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.

If you want to see old seminars: Videos of Past Conferences/Seminars

As summer approaches and vaccines become more and more available throughout the world, online seminars are slowly coming to an end. I will keep updating this list through the summer for all seminars that continue to stay active. (Seminars online now only include seminars which are active instead of all seminar series since some have stopped talked. If a seminar becomes active that is not on my list, let me know 馃榿)

For the autumn, it seems as though more universities will meet in person for small events (such as seminars) and therefore such an online list will no longer be needed. I will reassess the situation near the end of August to decide if this page will continue for another semester.

Thank you to all of you who helped add to the seminar list and who came to my site for updates on seminars! You're all epic.

鉂わ笍 Aram

I stand in solidarity with the black lives matter movement. You can read my full statement here.

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. 馃槂

- SSAC - Summer School of Algebraic Combinatorics
**21 - 25 June 2021** - CIRM: - Lattice Paths, Combinatorics and Interactions
**21 - 25 June 2021** - QTMC - Queer and Trans Mathematicians in Combinatorics
**24 - 25 June 2021** - Enhancing Equity Initiatives: - Climbing out of traps and tropes to make transformative change
**9 July 2021** - Women in Algebraic Combinatorics Research Community -
**Aug 5 - 6, 2021; Feb 10 - 11, 2022**

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

It is currently: **Mon 21 Jun 2021 14:15 UTC**

Last updated: Mon 21 Jun 2021 13:31 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 |
---|---|---|---|---|---|

Laura Colmenarejo (UMass Amherst) | Chromatic symmetric functions for Dyck paths and q-rook theory | Mon 21 Jun 2021 15:00 UTC | 50 minutes | Show | AGC |

Paula Kimmerling | Average Mixing Matrices of Trees and Stars | Mon 21 Jun 2021 15:30 UTC | 60 minutes | Show | AGT |

Veronica Ciocanel, Duke University | Modeling and topological data analysis for biological ring channels | Mon 21 Jun 2021 18:00 UTC | 50 minutes | Show | Michigan State |

Sebastian Wiederrecht | Even Circuits in Oriented Matroids | Mon 21 Jun 2021 19:00 UTC | 60 minutes | Show | MU |

Martin Vodicka (MPI MIS, Leipzig) | Geometry of Gaussian graphical model for the cycle | Tue 22 Jun 2021 08:00 UTC | 45 minutes | Show | NASO |

Rosa Winter | Recovery from power sums | Tue 22 Jun 2021 09:00 UTC | 45 minutes | Show | NASO |

Hankyung Ko | Monoidal actions of the Hecke category and Kostant's problem | Wed 23 Jun 2021 15:00 UTC | 60 minutes | Show | RepNet |

Terrence George (Michigan) | Arctic curves for groves | Thu 24 Jun 2021 17:00 UTC | 50 minutes | No abstract available | ACS |

Qiang Ye, University of Kentucky | Batch Normalization and Preconditioning for Neural Network Training | Thu 24 Jun 2021 18:30 UTC | 50 minutes | Show | Michigan State |

Isabelle Shankar (MPI MIS, Leipzig) | Symmetry Adapted Gram Spectrahedra | Fri 25 Jun 2021 08:00 UTC | 45 minutes | Show | NASO |

Leonid Monin (MPI MIS, Leipzig) | Macaulay inverse systems and computation of cohomology rings | Fri 25 Jun 2021 09:00 UTC | 45 minutes | Show | NASO |

Juanita Pinz贸n Caicedo (University of Notre Dame) | Variedades diferenciales de dimensi贸n cuatro y concordancia de nudos | Fri 25 Jun 2021 16:00 UTC | 60 minutes | Show | Cibercoloquio |

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

Steve Kirkland | TBA | Mon 28 Jun 2021 15:30 UTC | Check Seminar Page | No abstract available | AGT |

Lori Ziegelmeier, Macalester College | Capturing Dynamics of Time-Varying Data via Topology | Mon 28 Jun 2021 18:30 UTC | 50 minutes | Show | Michigan State |

Carla Groenland | TBA | Mon 28 Jun 2021 19:00 UTC | Check Seminar Page | No abstract available | MU |

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

Lord Kavi | TBA | Mon 05 Jul 2021 15:30 UTC | Check Seminar Page | No abstract available | AGT |

Nicolle Gonzalez (UCLA) | TBA | Mon 12 Jul 2021 15:00 UTC | 50 minutes | No abstract available | AGC |

Seminar Code | Name | Institution | Website |
---|---|---|---|

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

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

LUMS | John Conway Spirited Seminar Series | Lahore University of Management Sciences | Seminar Website |

MU | Online Matroid Theory Seminar | Matroid Union | Seminar Website |

NASO | Nonlinear Algebra Seminar Online | Max-Planck-Instut f眉r Mathematik (MPI) | Seminar Website |

Michigan State | Combinatorics and Graph Theory | Michigan State University | Seminar Website |

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

Cibercoloquio | Cibercoloquio Latinoamericano de Mathem谩ticas | Online | Seminar Website |

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

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

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

SemACT | Seminario de 脕lgebra, Combinatoria y Teor铆a de Lie | Universidad Nacional del Sur | Seminar Website |

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

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

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

Given a graph and a set of colors, a coloring is a function that associates each vertex in the graph with a color. In 1995, Stanley generalized this definition to symmetric functions by looking at the number of times each color is used and extending the set of colors to $\mathbb{Z}^+$. In 2012, Shareshian and Wachs introduced a refinement of the chromatic functions for ordered graphs as q-analogues.

In the particular case of Dyck paths, Stanley and Stembridge described the connection between chromatic symmetric functions of abelian Dyck paths and square hit numbers, and Guay-Paquet described their relation to rectangular hit numbers. Recently, Abreu-Nigro generalized the former connection for the Shareshian-Wachs q-analogue, and in unpublished work, Guay-Paquet generalized the latter.

In this talk, I want to give an overview of the framework and present another proof of Guay-Paquet's identity using q-rook theory. Along the way, we will also discuss q-hit numbers, two variants of their statistic, and some deletion-contraction relations. This is recent work with Alejandro H. Morales and Greta Panova.

We define the average mixing matrix (AMM) of a continuous-time quantum walk on a graph using the orthogonal projections onto the eigenspaces of the adjacency matrix A. From there, one of the properties that has been studied is the rank of the AMM. This is easiest to do if the eigenvalues of A are simple, and we鈥檒l review some of the results on this from Coutinho et. al. (2018). Then we鈥檒l see how Godsil et. al. (2018) used these and other methods to prove properties about the rank of AMM for trees. A special case of tree graphs is the star graph, which does not have simple eigenvalues and thus the bounds on the rank no longer apply. We鈥檒l show instead that the star graphs have full rank, which we proved in joint work with Dr. Judi McDonald but appears in Godsil et. al. (2018).

CloseActin filaments are polymers that interact with motor proteins inside cells and play important roles in cell motility, shape, and development. Depending on its function, this dynamic network of interacting proteins reshapes and organizes in a variety of structures, including bundles, clusters, and contractile rings. Motivated by observations from the reproductive system of the roundworm C. elegans, we use an agent-based modeling framework to simulate interactions between actin filaments and motor proteins inside cells. We also develop tools based on topological data analysis to understand time-series data extracted from these filamentous network interactions. We use these tools to compare the filament organization resulting from motors with different properties. We are currently interested in gaining insights into myosin motor regulation and the resulting actin architectures during cell cycle progression. This work also raises questions about how to assess the significance of topological features in topological summaries such as persistence diagrams.

CloseThis work generalises the even directed cycle problem, which asks whether a given digraph contains a directed cycle of even length, to orientations of regular matroids. We define non-even oriented matroids generalising non-even digraphs, which played a central role in resolving the computational complexity of the even dicycle problem. Then we show that the problem of detecting an even directed circuit in a regular matroid is polynomially equivalent to the recognition of non-even oriented matroids.

Our main result is a precise characterisation of the class of non-even oriented bond matroids in terms of forbidden minors, which complements an existing characterisation of non-even oriented graphic matroids by Seymour and Thomassen and reveals an extended class of obstructions.

This is joint work with Karl Heuer and Raphael Steiner.

In statistics, linear concentration model is given by the linear space of the symmetric matrices. Given the linear space L, there are two interesting numbers: The degree of variety $L^{-1}$, obtained by inverting all matrices in L and ML-degree of the model. It was shown that for general space L these two numbers are the same. However, this is not true for some specific spaces L. In this talk we will discuss such a case when L is the space for the Gaussian graphical model for the cycle. In this case these two numbers are different. We will focus on the degree of the variety $L^{-1}$ for which there is an explicit formula, conjectured by Sturmfels and Uhler, which we were able to prove. The proof is based on the intersection theory in the space of complete quadrics, intersection theory in Grassmannian and a lot of combinatorics.

CloseIn this talk I will speak about ongoing work with Hana Mel谩nov谩 and Bernd Sturmfels, in which we study the problem of recovering a collection of n numbers from the evaluation of m power sums. The polynomial system corresponds to intersecting Fermat hypersurfaces, and it can be underconstrained (m < n), square (m=n), or overconstrained (m > n). Questions that we ask are for example, when is recovery possible? If it is possible, is it unique? If it is not unique, can we give an upper bound for the number of solutions? I will present some results, and many more conjectures.

CloseLet g be a semisimple complex Lie algebra and let M be a g-module. Consider A(M), the space of linear endomorphisms on M on which the adjoint action of g is finite. A classical question of Kostant is: for which simple module M is the canonical map from U(g) to A(M) surjective? I will reformulate this problem using the language of monoidal (or 2-)categories. If M belongs to the BGG category O, then the answer to the problem is equivalent to equivalence of certain categorical actions of the Hecke category, and is determined by decomposing the action of translation functors on M. This leads to a conjectural answer to Kostant's problem in terms of the Kazhdan-Lusztig basis for the Hecke algebra. This is a joint work with Walter Mazorchuk and Rafael Mrden.

CloseBatch normalization (BN) is a popular and ubiquitous method in deep neural network training that has been shown to decrease training time and improve generalization performance. Despite its success, BN is not theoretically well understood. It is not suitable for use with very small mini-batch sizes or online learning. In this talk, we will review BN and present a preconditioning method called Batch Normalization Preconditioning (BNP) to accelerate neural network training. We will analyze the effects of mini-batch statistics of a hidden variable on the Hessian matrix of a loss function and propose a parameter transformation that is equivalent to normalizing the hidden variables to improve the conditioning of the Hessian. Compared with BN, one benefit of BNP is that it is not constrained on the mini-batch size and works in the online learning setting. We will present several experiments demonstrating competitiveness of BNP. Furthermore, we will discuss a connection to BN which provides theoretical insights on how BN improves training and how BN is applied to special architectures such as convolutional neural networks. The talk is based on a joint work with Susanna Lange and Kyle Helfrich.

CloseSum of squares (SOS) relaxations are often used to certify nonnegativity of polynomials and are equivalent to solving a semidefinite program (SDP). The feasible region of the SDP for a given polynomial is the Gram Spectrahedron. For symmetric polynomials, there are reductions to the problem size that can be done using tools from representation theory. In joint work with Serkan Hosten and Alexander Heaton, we investigate the geometric structure of the spectrahedra that arise in the study of symmetric SOS polynomials, the Symmetry Adapted PSD cone and the Symmetry Adapted Gram Spectrahedron.

CloseIt was observed by Pukhlikov and Khovanskii that the BKK theorem implies that the volume polynomial on the space of polytopes is the Macaulay generator of the cohomology ring of a smooth projective toric variety. This provides a way to express the cohomology ring of toric variety as a quotient of the ring of differential operators with constant coefficients by the annihilator of an explicit polynomial. The crucial ingredient of this observation is an explicit expression for the Macaulay generator of graded Gorenstein algebras generated in degree 1.

In my talk I will explain this construction in detail, then I will tell about recent results on explicit expression for the Macauley generator of an arbitrary algebra with Gorenstein duality. Finally, if time permits, I will show how these results yield to the computation of the cohomology rings of more general classes of algebraic varieties.

El objetivo principal de la topolog铆a geom茅trica es la clasificaci贸n de variedades diferenciales dentro de un marco determinado (topol贸gico, suave, simplemente conexo, simpl茅ctico, etc.). La dimensi贸n cuatro es especial, ya que es la 煤nica dimensi贸n en la que una variedad puede admitir un n煤mero infinito de estructuras suaves no equivalentes, y la 煤nica dimensi贸n en la que existen variedades homeomorfas pero no difeomorfas a R^4. A su vez, la concordancia de nudos es el estudio de nudos como fronteras de superficies embebidas en espacios de dimensi贸n 4. La diferencia entre estructuras topol贸gicas y suaves se puede detectar a trav茅s del estudio de la concordancia de nudos, y las operaciones satelitales son una herramienta poderosa para estudiar la estructura algebraica del grupo de concordancia de nudos. En la charla describir茅 c贸mo la teor铆a de gauge con grupo SO(3) proporciona un criterio que garantiza que la imagen de una operaci贸n satelital contenga un subgrupo de rango infinito.

CloseOne approach to understanding complex data is to study its shape through the lens of algebraic topology. While the early development of topological data analysis focused primarily on static data, in recent years, theoretical and applied studies have turned to data that varies in time. A time-varying collection of metric spaces as formed, for example, by a moving school of fish or flock of birds, can contain a vast amount of information. There is often a need to simplify or summarize the dynamic behavior. One such method is a crocker plot, a 2-dimensional image that displays the (non-persistent but varying with scale) topological information at all times simultaneously. We use this method to perform exploratory data analysis and investigate parameter recovery via machine learning in the collective motion model of D鈥橭rsogna et al. (2006). Then, we use it to choose between unbiased correlated random walk models of Nilsen et al. (2013) that describe motion tracking experiments on pea aphids. We then introduce a new tool to summarize time-varying metric spaces: a crocker stack. Crocker stacks are convenient for visualization, amenable to machine learning, and satisfy a stability property.

Close