If you'd like to submit a talk, you can either email Aram directly or fill out this form. Only talks within the next week or two will be here in order to keep the list readable.

If you prefer actually using a calendar, Ao Sun and Mingchen Xia are uploading everything onto google calendar. You can check it out here.

Alternatively, if you want to see math seminars of all disciplines, you can try the following website.

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. ðŸ˜ƒ

- ACOW - Algebraic Combinatorics Online Workshop.
**20-30 April 2020** - DMD 2020 - Discrete Matheamtics 2-Day at Albany.
**25-26 April 2020** - AlCoVE - an Algebraic Combinatorics Virtual Expedition.
**15-16 June 2020** - FPSAC 2020 Online - Formal Power Series and Algebraic Combinatorics 2020 Online.
**6-24 July 2020**

All times are denoted in your local computer time.

It is currently: **Thu 28 May 2020 08:47 UTC**

Last updated: Mon 25 May 2020 12:00 UTC

Green - Talk is currently happening.

Yellow - Talk is coming up within the hour.

Red - Talk is in under 10 minutes.

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

Helen Jenne (University of Oregon) | TBA | Thu 28 May 2020 18:30 UTC | Check Seminar Page | View Seminar page | No abstract available | 18 |

Ben Young (University of Oregon) | TBA | Thu 28 May 2020 19:15 UTC | Check Seminar Page | View Seminar page | No abstract available | 18 |

Benjamin Young (Oregon) | TBA | Fri 29 May 2020 15:00 UTC | 60 minutes | Zoom Link | No abstract available | 21 |

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

Digjoy Paul (HBNI) | New approaches to the restriction problem | Mon 01 Jun 2020 15:00 UTC | 50 minutes | Zoom Link | Show | 23 |

Iva Halacheva (Northeastern University) | TBA | Mon 01 Jun 2020 20:10 UTC | 50 minutes | Zoom link. Please contact Eugene Gorsky or JosÃ© Simental RodrÃguez for password. | No abstract available | 16 |

Igor Pak | Combinapakorics | Tue 02 Jun 2020 12:00 UTC | 60 minutes | View Seminar page | No abstract available | 6 |

Wojciech Samotij (Tel Aviv) | An entropy proof of the ErdÅ‘s-Kleitman-Rothschild theorem. | Tue 02 Jun 2020 13:00 UTC | Check Seminar Page | View Seminar page | Show | 11 |

Jean Bertoin (University of ZÃ¼rich) | Scaling exponents of step-reinforced random walks | Tue 02 Jun 2020 14:30 UTC | Check Seminar Page | View Seminar page | Show | 11 |

Tim Seynnaeve (MPI MIS, Leipzig) | TBA | Tue 02 Jun 2020 15:00 UTC | 30 minutes | View Seminar page | No abstract available | 9 |

He Guo (Georgia Tech) | Packing nearly optimal Ramsey $R(3, t)$ graphs | Wed 03 Jun 2020 17:00 UTC | 60 minutes | Meeting ID: 268 276 468 Password: How many ways are there to rearrange the letters in GOCC? | Show | 4 |

Liana Yepremyan ( London School of Economics and Political Science, University of Illinois at Chicago) | Ryserâ€™s conjecture and more | Fri 05 Jun 2020 15:00 UTC | 60 minutes | View Seminar page | Show | 21 |

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

Deniz Kus (Ruhr-University Bochum) | TBA | Thu 11 Jun 2020 15:00 UTC | Check Seminar Page | Zoom Meeting ID: 894 0978 8415 | No abstract available | 5 |

Inna Entova (Ben Gurion University) | TBA | Thu 25 Jun 2020 15:00 UTC | Check Seminar Page | Zoom Meeting ID: 894 0978 8415 | No abstract available | 5 |

Gregory G. Smith (Queen's) | The geometry of smooth Hilbert schemes | Mon 29 Jun 2020 15:00 UTC | 50 minutes | View Seminar page | No abstract available | 1 |

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

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

2 | New York Combinatorics Seminar | CUNY | Seminar Website |

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

4 | Graduate Online Combinatorics Colloquium | GOCC | Seminar Website |

5 | Algebraic Combinatorics Seminar | IMSc | Seminar Website |

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

7 | Virtual seminar on algebraic matroids and rigidity theory | MIT | Seminar Website |

8 | Online Matroid Theory Seminar | Matroid Union | Seminar Website |

9 | Nonlinear Algebra Seminar Online | Max-Planck-Instut fÃ¼r Mathematik (MPI) | Seminar Website |

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

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

12 | Combinatorics Lectures Online | Princeton University | Seminar Website |

13 | Rutgers Experimental Mathematics Seminar | Rutgers University | Seminar Website |

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

15 | Combinatorics Seminar | UC Berkeley | Seminar Website |

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

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

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

19 | Combinatorics Seminar | University of Minnesota | Seminar Website |

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

21 | SÃ©minaire de combinatoire et d'informatique mathÃ©matique du LaCIM | UniversitÃ© du QuÃ©bec Ã MontrÃ©al | Seminar Website |

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

23 | Applied Algebra Seminar | York University | Seminar Website |

Digjoy Paul (HBNI)

**New approaches to the restriction problem**

Given an irreducible polynomial representation $W_n$ of the general linear group $GL_n$, we can restrict it to the representations of the symmetric group $S_n$ that seats inside $GL_n$ as a subgroup. The restriction problem is to find a combinatorial interpretation of the restriction coefficient: the multiplicity of an irreducible $S_n$ modules in such restriction of $W_n$. This is an open problem (see OPAC 2021!) in algebraic combinatorics. In Polynomial Induction and the Restriction Problem, we construct the polynomial induction functor, which is the right adjoint to the restriction functor from the category of polynomial representations of $GL_n$ to the category of representations of $S_n$. This construction leads to a representation-theoretic proof of Littlewood's Plethystic formula for the restriction coefficient. Character polynomials have been used to study characters of families of representations of symmetric groups (see Garsia and Goupil ), also used in the context of FI-modules by Church, Ellenberg, and Farb (see FI-modules and stability for representations of symmetric groups). In Character Polynomials and the Restriction Problem, we compute character polynomial for the family of restrictions of $W_n$ as $n$ varies. We give an interpretation of the restriction coefficient as a moment of a certain character polynomial. To characterize partitions for which the corresponding Weyl module has non zero $S_n$-invariant vectors is quite hard. We solve this problem for partition with two rows, two columns, and for hook-partitions.

CloseWojciech Samotij (Tel Aviv)

**An entropy proof of the ErdÅ‘s-Kleitman-Rothschild theorem.**

We say that a graph G is H-free if G does not contain H as a (not necessarily induced) subgraph. For a positive integer n, denote by ex(n,H) the largest number of edges in an H-free graph with n vertices (the TurÃ¡n number of H). The classical theorem of ErdÅ‘s, Kleitman, and Rothschild states that, for every râ‰¥3, there are 2ex(n,H)+o(n2) many Kr-free graphs with vertex set {1,â€¦, n}. There exist (at least) three different derivations of this estimate in the literature: an inductive argument based on the KÅ‘vÃ¡ri-SÃ³s-TurÃ¡n theorem (and its generalisation to hypergraphs due to ErdÅ‘s), a proof based on SzemerÃ©di's regularity lemma, and an argument based on the hypergraph container theorems. In this talk, we present yet another proof of this bound that exploits connections between entropy and independence. This argument is an adaptation of a method developed in a joint work with Gady Kozma, Tom Meyerovitch, and Ron Peled that studied random metric spaces.

CloseJean Bertoin (University of ZÃ¼rich)

**Scaling exponents of step-reinforced random walks**

Let X1, â€¦ be i.i.d. copies of some real random variable X. For any Îµ2, Îµ3, â€¦ in {0,1}, a basic algorithm introduced by H.A. Simon yields a reinforced sequence XÌ‚1, XÌ‚2, â€¦ as follows. If Îµn=0, then XÌ‚n is a uniform random sample from XÌ‚1, â€¦, XÌ‚n-1; otherwise XÌ‚n is a new independent copy of X. The purpose of this talk is to compare the scaling exponent of the usual random walk S(n)=X1 +â€¦ + Xn with that of its step reinforced version SÌ‚(n)=XÌ‚1+â€¦ + XÌ‚n. Depending on the tail of X and on asymptotic behavior of the sequence Îµj, we show that step reinforcement may speed up the walk, or at the contrary slow it down, or also does not affect the scaling exponent at all. Our motivation partly stems from the study of random walks with memory, notably the so-called elephant random walk and its variations.

CloseHe Guo (Georgia Tech)

**Packing nearly optimal Ramsey $R(3, t)$ graphs**

In 1995 Kim famously proved the Ramsey bound $R(3, t) â‰¥ ct^2/\log t$ by constructing an $n$-vertex graph that is triangle-free and has independence number at most $C\sqrt{n \log n}$. We extend this celebrated result, which is best possible up to the value of the constants, by approximately decomposing the complete graph $K_n$ into a packing of such nearly optimal Ramsey $R(3, t)$ graphs.

More precisely, for any $\varepsilon > 0$ we find an edge-disjoint collection $(G_i)_i$ of n-vertex graphs $G_i \subseteq K_n$ such that (a) each $G_i$ is triangle-free and has independence number at most $C_\varepsilon \sqrt{n \log n}$, and (b) the union of all the $G_i$ contains at least $(1 âˆ’ \varepsilon ) \binom{n}{2}$ edges. Our algorithmic proof proceeds by sequentially choosing the graphs $G_i$ via a semi-random (i.e., RÃ¶dl nibble type) variation of the triangle-free process.

As an application, we prove a conjecture in Ramsey theory by Fox, Grinshpun, Liebenau, Person, and SzabÃ³ (concerning a Ramsey-type parameter introduced by Burr, ErdÃ¶s, LovÃ¡sz in 1976). Namely, denoting by $s_r(H)$ the smallest minimum degree of $r$-Ramsey minimal graphs for $H$, we close the existing logarithmic gap for $H = K_3$ and establish that $s_r(K_3) = \Theta(r^2 \log r)$.

Based on joint work with Lutz Warnke. And the paper can be found at Combinatorica 40 (2020), 63â€“103.

Liana Yepremyan ( London School of Economics and Political Science, University of Illinois at Chicago)

**Ryserâ€™s conjecture and more**

A Latin square of order $n$ is an $n \times n$ array filled with $n$ symbols such that each symbol appears only once in every row or column and a transversal is a collection of cells which do not share the same row, column or symbol. The study of Latin squares goes back more than 200 years to the work of Euler. One of the most famous open problems in this area is a conjecture of Ryser, Brualdi and Stein from 60s which says that every Latin square of order $n\times n$ contains a transversal of order $n-1$. A closely related problem is 40 year old conjecture of Brouwer that every Steiner triple system of order $n$ contains a matching of size $(n-4)/3$. The third problem weâ€™d like to mention asks how many distinct symbols in Latin arrays suffice to guarantee a full transversal? In this talk we discuss a novel approach to attack these problems.

Joint work with Peter Keevash, Alexey Pokrovskiy and Benny Sudakov.