New York Combinatorics Seminar

This seminar is sponsored by the CUNY Graduate Center's Math Department and Computer Science Department. It covers a wide range of topics in combinatorics and its applications. 

Fridays from Noon till 1:00 pm ET 

The CUNY Graduate Center is located at 365 Fifth Avenue (at the corner of 34th Street), New York. It can be easily reached by subway using the B,D,F,N,Q,R, or 6 train.

Seminar Co-Organizers (alphabetically):  Kira Adaricheva (Hofstra) Deepak Bal (Montclair State) Nadia Benakli (City Tech) Jonathan Cutler (Montclair State) Ezra Halleck (City Tech), Sandra Kingan (Graduate Center & Brooklyn College), Joseph Malkevitch (Graduate Center & York College), Kerry Ojakian (BCC), Megan Owen ( Graduate Center &Lehman College), Anna Pun (Baruch College), Abigail Raz (Cooper Union) Eric Rowland (Hofstra) Mingxian Zhong (Graduate Center & Lehman College).

Spring 2023 Talks

Zoom Link forSpring 2023 Virtual Talks:  
The link changes every semester, but the password stays the same. In person talks are specified in red.

Feb 10, 2023: Vinayak Joshi (Savitribai Phule Pune University, India) 

Title : Chordal and Perfect zero-divisor graphs of posets and applications to graphs associated with algebraic structures

Abstract: In this talk, we discuss the characterizations of the perfect zero-divisor graphs and chordal zero-divisor graphs (its complement) of ordered sets. These results are applied to the zero-divisor graphs of finite reduced rings, the comaximal ideal graphs of rings, the annihilating ideal graphs, the intersection graphs of ideals of rings, and the intersection graphs of subgroups of groups. In fact, it is shown that these graphs associated with a commutative ring R with identity can be effectively studied via the zero-divisor graph of a specially constructed poset from R.

Feb 17, 2023: No Talk

Feb 24, 2023: Sheila Sundaram

Title: Schur-positivity of power sums

Abstract: We investigate the Schur-positivity of sums of power sum symmetric functions, in particular those corresponding to rectangular partitions.  We show that these have a nice description in terms of the representations induced from the subgroup generated by the long cycle  of the symmetric group.  The number-theoretic Ramanujan sum is an important ingredient of these representations.  Parts of this talk are based on recent joint work with John Shareshian.

Mar 3, 2023: Sergi Elizalde (Dartmouth University)

Title: Descents on noncrossing and nonnesting permutations

Abstract: Stirling permutations were introduced by Gessel and Stanley to give a combinatorial interpretation of certain polynomials related to Stirling numbers, which count set partitions with a given number of blocks. A natural extension of Stirling permutations are noncrossing (also called quasi-Stirling) permutations, which are in bijection with labeled rooted plane trees. Archer et al. introduced these permutations, and conjectured that there are (n+1)^(n-1) such permutations of size n having n descents. In this talk we prove this conjecture, and we find the generating function for noncrossing permutations by the number of descents. We show that some of the properties of descents on usual permutations and on Stirling permutations have an analogue for noncrossing permutations.  Finally, we consider a nonnesting analogue, and we show that the polynomial giving the distribution of the number of descents on nonnesting permutations is a product of an Eulerian polynomial and a Narayana polynomial. It follows that, rather unexpectedly, this polynomial is palindromic.

Mar 10, 2023: Richard Stanley (Massachusetts Institute of Technology)

Mar 17, 2023: Hermie Monterde (University of Manitoba)

Mar 24, 2023: Zachary Hamaker (University of Florida)

Mar 31, 2023: Maria Chudnovsky (Princeton University) in person

Apr 7, 2023: Spring Break

Apr 14, 2023: J B Nation (University of Hawaii)

Title:  The maximum size of deletion error correcting codes

Abstract: What is the largest size of a length n binary code that can correct t deletion errors? This talk will explain deletion error correcting codes and report some recent progress on this still-open question by various members of the coding theory community. 

Apr 21, 2023: Csaba Biro (University of Louisville)

Apr 28, 2023: No Talk

May 5, 2023:

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Previous Speakers

Fall 2022
Spring 2022
Fall 2021
Spring 2021
Fall 2020
Spring 2020
Fall 2019
Spring 2019
Fall 2018
Spring and Summer 2018
Fall 2017
Spring 2017
Fall 2016
Spring 2016
Fall 2015
Spring 2015
Fall 2014
Spring 2014
Fall 2013
Spring 2013
Fall 2012
Spring 2012
Fall 2011
Spring 2011
Previous Talks hosted by Janos Pach