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

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

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

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.

/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 )

https://dept-info.labri.fr/~gavoille/

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 ] .

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.

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

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

Abstract: TBA

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

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

Abstract: TBA

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

Lecture held in MS 7608.
Abstract: TBA

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

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

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

Abstract: TBA

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

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

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

Abstract: TBA

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

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.

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

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

Abstract: TBA