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--- seminars:comb:start [2026/02/16 15:12]
zaslav [SPRING 2026]
+++ seminars:comb:start [2026/03/25 15:18] (current)
zaslav [SPRING 2026]
@@ Line 70: / Line 70: @@
 **Tuesday, 2/24**\\
 Speaker: Xiyong Yan (Binghamton)\\
-Title: \\
+Title: Signs of Hamiltonian Circles in Simple Plane Signed Graphs \\
 Time: 1:30-2:30\\
 Location:  WH 100E
+I study the signs of Hamiltonian circles in simple plane signed graphs by expressing the sign of a Hamiltonian circle as the product of the signs of the faces it encloses. This leads to the notion of co-Hamiltonian sequences and to a criterion for the existence of Hamiltonian circles of opposite sign, based on sequences whose enclosed face-products have opposite signs. Signed rectangular grid graphs form a natural subclass. For $m \times n$ grids with $m$ even and $m,n>3$, I prove the following theorem. All Hamiltonian circles have the same sign if and only if all non-corner boxes have the same sign. Motivated by the grid structure, I also develop local structural theorems, including ladder-type and hexagon configurations, that guarantee the existence of both positive and negative Hamiltonian circles without explicitly constructing full co-Hamiltonian sequences.
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 **Tuesday, 3/3**\\
-Speaker: Thomas Galvin (Binghamton)\\
+Speaker: Patrick <html>Sol&eacute;</html> (CNRS, Marseille)\\
-Title: \\
+Title: Perfect Codes in Weakly Metric Association Schemes\\
 Time: 1:30-2:30\\
-Location:  WH 100E
+Location:  WH 100E and Zoom https://binghamton.zoom.us/j/94050971055?pwd=nmry51RPN2IUT4N2FfK9UxSljuJtqX.1
+The Lloyd Theorem of (<html>Sol&eacute;</html>, 1989) is combined with the Schwartz--Zippel Lemma of theoretical computer science to derive non-existence results for perfect codes in the Lee metric, NRT metric, mixed Hamming metric, and for the sum-rank distance. The proofs are based on asymptotic enumeration of integer partitions. The framework is the new concept of {polynomial} weakly metric association schemes.
+A connection between this notion and the recent theory of multivariate P-polynomial schemes of (Bannai et al., 2025) and of $m$-distance regular graphs (Bernard et al., 2025) is pointed out.
+(This is joint work with Minjia Shi and Jing Wang.)
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 **Tuesday, 3/10**\\
 Speaker: Aida Abiad (Amsterdam)\\
-Title: \\
+Title: On weight-equitable partitions and their application to graph theory\\
 Time: 1:30-2:30\\
-Location:  WH 100E and Zoom
+Location:  WH 100E and Zoom  https://binghamton.zoom.us/j/94050971055?pwd=nmry51RPN2IUT4N2FfK9UxSljuJtqX.1
+Weight-equitable partitions of graphs, which are a natural extension of the well-known equitable partitions, have been shown to be a powerful tool to weaken the regularity assumption in several classic eigenvalue bounds. Weight-equitable partitions assign to each vertex a weight that equals the corresponding entry of the Perron eigenvector.  In this talk, I will present several applications of such partitions to graph theory problems.
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 **Tuesday, 3/17**\\
-Speaker: \\
+Speaker: Thomas Galvin (Binghamton)\\
-Title: \\
+Title: Edge Ideals & Graph Matching\\
 Time: 1:30-2:30\\
 Location:  WH 100E
+For a simple graph G, the edge ideal I(G) over a field K is a monomial ideal generated by the edges of G. The associated primes of powers of such ideals form an ascending chain. In this talk, I prove a key ingredient of this result, concerning maximum matchings of graphs derived from G. The talk is based on a paper by Martínez-Bernal, Morey, and Villarreal (2012).
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 **Tuesday, 3/24**\\
 Speaker: Thomas Martinez (UCLA and Cornell) \\
-Title: \\
+Title: The Combinatorics of Affine Deodhar Diagrams\\
 Time: 1:30-2:30\\
 Location:  WH 100E
+Deodhar diagrams (also known as Go diagrams) have been studied due to their relation to the totally non-negative Grassmannian and positroid varieties. In this talk, we introduce affine Deodhar diagrams and study combinatorial moves of these diagrams. We provide geometric analogues of our combinatorial moves, discussing the relationship to (affine patches of) positroid varieties and their cluster structure.
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 **Tuesday, 4/21**\\
-Speaker: \\
+Speaker: Xiyong Yan (Binghamton)\\
-Title: \\
+Title: Candidacy exam\\
 Time: 1:30-2:30\\
 Location:  WH 100E
+This is Mr. Yan's candidacy exam.  The examining committee consists of Laura Anderson, Michael Dobbins, and Thomas Zaslavsky (chair).  The talks are open to all.
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 **Tuesday, 4/28**\\
-Speaker: \\
+Speaker: Alireza Salahshoori (Binghamton)\\
-Title: \\
+Title: (Candidacy exam)\\
 Time: 1:30-2:30\\
 Location:  WH 100E
+This is Mr. Salahshoori's candidacy exam.  The examining committee consists of Laura Anderson, Michael Dobbins, and Thomas Zaslavsky (chair).  The talks are open to all.
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 **Tuesday, 5/5**\\
-Speaker: \\
+Speaker: Danika Van Niel (Binghamton) \\
 Title: \\
 Time: 1:30-2:30\\
+Location:  WH 100E
+<HTML><li></HTML>
+**Thursday, 5/7 (Colloquium)**\\
+Speaker: Isabella Novik (Washington) \\
+Title: \\
+Time: \\
 Location:  WH 100E

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