Organizers: Laura Anderson, Vaidy Sivaraman, and Thomas Zaslavsky.

**Tuesday, January 28**

*Speaker*: Dillon Mayhew (Victoria University of Wellington, visiting Princeton)

*Title*: Some Approaches to Characterizing Representable Matroids

*Time*: 1:15 - 2:15

*Room*: LN-2205**Tuesday, February 4**

Organizational meeting

*Time*: 1:15 - 2:15

*Room*: LN-2205**Tuesday, February 11**

*Speaker*: Laura Anderson (Binghamton)

*Title*: Introduction to Matroid Polytopes

*Time*: 1:15 - 2:15

*Room*: LN-2205**Tuesday, February 18**

*Speaker*: Melissa Fuentes (Binghamton)

*Title*: Proper Connection of Graphs

*Time*: 1:15 - 2:15

*Room*: LN-2205**Tuesday, February 25**

*Speaker*: Marcelo Aguiar (Cornell)

*Title*: The Ring of Graphs and the Chromatic Polynomial

*Time*: 1:15 - 2:15

*Room*: LN-2205**Tuesday, March 4**(joint with the Algebra Seminar)

*Speaker*: Luise-Charlotte Kappe (Binghamton)

*Title*: On the Covering Number of Small Symmetric Groups and the Erdös-Ko-Rado Theorem**Tuesday, March 11***Speaker*: Thomas Zaslavsky (Binghamton)*Title*: Geometry and the Chess Pieces*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, March 18***Speaker*: Vaidy Sivaraman (Binghamton)*Title*: Important Conjectures and Problems I Like*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, March 25***Speaker*: Laura Anderson (Binghamton)*Title*: Positroids? Did you say "Positroids"?*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, April 1***Speaker*: Richard Behr (Binghamton)*Title*: An Introduction to Threshold Graphs*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, April 8 (joint with the Geometry/Topology Seminar)***Speaker*: Jay Schweig (Oklahoma State)*Title*: Bounding the Homology of a Simplicial Complex*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, April 15**

Spring Break**Tuesday, April 22***Speaker*: Peter Maceli (Columbia)*Title*: Coloring Graphs with Forbidden Induced Subgraphs*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, April 29***Speaker*: L. William Kazmierczak (Stevens and Binghamton)*Title*: Node Vulnerability Models for Graph Theoretic Networks*Time*: 1:15 - 2:15*Room*: LN-2205**Tuesday, May 6***Title*: Problem session*Time*: 1:15 - 2:15*Room*: LN-2205**Thursday, May 15 (Note special day)***Speaker*: Ting Su (Binghamton)*Title*: Extremal Edge Polytopes of Graphs*Time*: 11:00 - 12:00**(Note special time)***Room*: LN-2201**Thursday, June 19 (Note special day)***Speaker*: Sonja Riedel (Bremen)*Title*: Combinatorial Invariants of Toric Hyperplane Arrangements*Time*: 2:00 - 3:00**(Note unusual time)***Room*: LN-2205 (Note usual room)A 'toric hyperplane arrangement' A is a finite family of 'toric hyperplanes', that is, hypersurfaces in the n-dimensional torus (C

^{*})^{n}(complex, noncompact) or (S^{1})^{n}(real, compact) that are analogous to hyperplanes in real or complex linear space. Thus, toric hyperplane arrangements are analogues of ordinary hyperplane arrangements, which are finite sets of hyperplanes in a vector space.Recent work of De Concini and Procesi generated new interest in combinatorial invariants of the topology of the complement of A. In the case of so-called 'complexified real' toric arrangements, the induced stratification of the compact torus (S

^{1})^{n}(which is the decomposition of the torus into the faces of the arrangement) determines the homotopy type of the complement. To establish in greater generality the link between the combinatorics of these face structures and the topology of A I use the techniques of matroid theory. Starting from the theory of semimatroids and oriented matroids, I want to develop a 'toric oriented matroid' with the goal of characterizing the face structure of the stratification.The talk will include an introduction to toric arrangements and the necessary background in matroid theory.

*Speaker*: Jim Lawrence (George Mason)

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