# List of upcoming online seminars in discrete mathematics, combinatorics, and graph theory

Here is a list of upcoming online seminars in combinatorics, automatically generated from researchseminars.org and a few other calendars available in the iCal format. Please let me know if you find any interesting iCal feed / Google Calendar of the seminars.

You can also find a list of upcoming workshops, conferences, and schools.

Timezone: Korea (KST), UTC/GMT+9.

### October 2022

#### October 4

4:30 pm – 5:30 pm

Title: On the degenerate Turán problems
by Zixiang Xu (IBS Extremal Combinatorics and Probability Group) as part of IBS/KAIST Discrete Math Seminar

View-only livestream: https://www.youtube.com/c/ibsdimag
Lecture held in Room B232, IBS.
Abstract: TBA

#### October 6 11:15 pm – October 7 1:00 am

Title: Cluster structures for Grassmannians
by Karin Baur (University of Leeds) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09

Abstract
The category of Cohen Macaulay modules over a quotient of a preprojective algebra is a cluster category associated to the coordinate ring of the Grassmannian Gr(k,n). We study this category and describe some of its indecomposable modules. We also explain how one can associate frieze patterns to them.

#### October 6

10:00 am – 11:00 am
Konstantin Tikhomirov (Carnegie Mellon University)

Title: A remark on the Ramsey number of the hypercube
by Konstantin Tikhomirov (Carnegie Mellon University) as part of IBS Virtual Discrete Math Colloquium

Abstract: TBA

#### October 7

6:00 am – 7:00 am
Eugene Gorsky (UC Davis)

Title: Cluster structures on braid varieties
by Eugene Gorsky (UC Davis) as part of UCLA Combinatorics Seminar

Lecture held in MS 7608.

Abstract
Given a positive braid, one can define a smooth affine algebraic variety called the braid variety. Braid varieties generalize several important varieties in Lie theory such as open Richardson and positroid varieties. I will construct a cluster structure on a braid variety of arbitrary type using combinatorial objects called weaves. This is a joint work with Roger Casals, Mikhail Gorsky, Ian Le, Linhui Shen and Jose Simental.

9:00 pm – 10:00 pm
[gt.go] - Smaller Universal Graphs for Caterpillars and Graphs of Bounded Path-Width by Cyril Gavoille

/Exposé en français/Talk in french / English slides / transparents en anglais

In this talk, I will given a rather simple construction of a graph U n with at most 8n vertices with the property that every n-vertex caterpillar is isomorphic to some induced-subgraph of U n . Previous constructions of so-called induced-universal graph for caterpillars used 256n vertices in the best (Bonichon et al. SIROCCO’06 and Alstrup et al. FOCS’15).

Then, I will also present an extension to path-width-p graphs with an induced-universal graph of n.2 O(p) vertices. This is complemented with a n.2 Ω(p) lower bound. With bounded path-width graphs, our construction considerably enlarge the family of n-vertex graphs having an induced-universal graph of O(n) vertices, which is optimal. Such unexpected property was known only for trees, bounded maximum degree outerplanar graphs and maximum degree-2 graphs.

The extended result is obtained from an algorithmic approach by designing an adjacency labeling scheme for these graphs using log(n) + O(p) bit vertex labels and with a constant time adjacency test.

This is a joint with Arnaud Labourel.

[Cyril Gavoille] (Université de Bordeaux, Labri )

Remarks / Remarques

Find all the information of the working group on this [ https://graphesetoptimisation.labri.fr/pmwiki.php/Groupe/GT?userlang=en | web page ] .
Retrouvez toutes les informations du GT sur cette [ https://graphesetoptimisation.labri.fr/pmwiki.php/Groupe/GT | page web ] .

#### October 8

12:00 am – 1:00 am
Jose Bastidas (LACIM)

Title: The primitive Eulerian polynomial
by Jose Bastidas (LACIM) as part of CRM-Séminaire du LACIM

Abstract
We introduce the Primitive Eulerian polynomial $P_\mathcal{A}(z)$ of a central hyperplane Arrangement $\mathcal{A}$. It is a reparametrization of the cocharacteristic polynomial of the arrangement. Previous work (2021) implicitly showed that this polynomial has nonnegative coefficients in the simplicial case. If $\mathcal{A}$ is the arrangement corresponding to a Coxeter group $W$ of type A or B, then $P_\mathcal{A}(z)$ is the generating function for the (flag)excedance statistic on a particular subset of $W$. No interpretation was found for reflection arrangements of type D.

We present an alternative geometric and combinatorial interpretation for the coefficients of $P_\mathcal{A}(z)$ for all simplicial arrangements $\mathcal{A}$. For reflection arrangements of types A, B, and D, we find recursive formulas that mirror those for the Eulerian polynomial of the corresponding type. We also present real-rootedness results and conjectures for $P_\mathcal{A}(z)$. This is joint work with Christophe Hohlweg and Franco Saliola.

#### October 11

4:30 pm – 5:30 pm

Title: Exact results for generalized extremal problems forbidding an even cycle
by Nika Salia (IBS Extremal Combinatorics and Probability Group) as part of IBS/KAIST Discrete Math Seminar

View-only livestream: https://www.youtube.com/c/ibsdimag
Lecture held in Room B232, IBS.
Abstract: TBA

#### October 13 11:15 pm – October 14 1:00 am

by Christian Haase (FU Berlin) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

#### October 13

4:00 pm – 5:30 pm
Nicholas Wormald (Monash University, Australia)

by Nicholas Wormald (Monash University, Australia) as part of Combinatorics Today Series – ITB

Abstract: TBA

#### October 18

4:30 pm – 5:30 pm

by Florent Koechlin (LORIA, INRIA, Nancy, France) as part of IBS/KAIST Discrete Math Seminar

View-only livestream: https://www.youtube.com/c/ibsdimag
Lecture held in Room B232, IBS.
Abstract: TBA

#### October 20 11:15 pm – October 21 1:00 am

by Lorenzo Vecchi (Università di Bologna) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

#### October 27 11:15 pm – October 28 1:00 am

by Søren Eilers (KU) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

#### October 27

4:00 pm – 5:30 pm
Edy Tri Baskoro (Institut Teknologi Bandung, Indonesia)

by Edy Tri Baskoro (Institut Teknologi Bandung, Indonesia) as part of Combinatorics Today Series – ITB

Abstract: TBA

#### October 28

6:00 am – 7:00 am
Daping Weng (UC Davis)

by Daping Weng (UC Davis) as part of UCLA Combinatorics Seminar

Lecture held in MS 7608.
Abstract: TBA

### November 2022

#### November 4

12:15 am – 2:00 am

by Leonid Monin (MPI MiS) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

#### November 11

12:15 am – 2:00 am

by Eva Philippe (IMJ-PRG) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

4:00 pm – 5:30 pm
Sang-il Oum (Institute for Basic Science and KAIST, South Korea)

by Sang-il Oum (Institute for Basic Science and KAIST, South Korea) as part of Combinatorics Today Series – ITB

Abstract: TBA

#### November 18

12:15 am – 2:00 am

by Boulos El Hilany (TU Braunschweig) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

#### November 25

12:15 am – 2:00 am

by Benjamin Nill (Otto-von-Guericke-Universität Magdeburg) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

4:00 pm – 5:30 pm
Nicolas Trotignon (CNRS, LIP, ENS de Lyon, France)

by Nicolas Trotignon (CNRS, LIP, ENS de Lyon, France) as part of Combinatorics Today Series – ITB

Abstract: TBA

### December 2022

#### December 2

12:15 am – 2:00 am

by Ayah Almousa (University of Minnesota – Twin Cities) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

#### December 9

12:15 am – 2:00 am

Title: Newton polytope of good symmetric functions
by Khanh Nguyen Duc (State University of New York at Albany) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09

Abstract
We introduce a general class of symmetric functions that has saturated Newton polytope and their Newton polytope has integer decomposition property. The class covers numerous previously studied symmetric functions.

#### December 16

12:15 am – 2:00 am

by Nick Early (MPI MiS) as part of Copenhagen-Jerusalem Combinatorics Seminar

Interactive livestream: https://ucph-ku.zoom.us/j/69204766431?pwd=bCtTczMzVEg2cG03cldKVjdvS09UUT09
Abstract: TBA

4:00 pm – 5:30 pm
Csilla Bujtás (University of Ljubljana, Ljubljana, Slovenia)

by Csilla Bujtás (University of Ljubljana, Ljubljana, Slovenia) as part of Combinatorics Today Series – ITB

Abstract: TBA