The Combinatorics Seminar

SPRING 2009

The usual day, time, and place are:

Tuesdays, 1:15 - 2:15, in

Room LN-2205,

with coffee, tea, and cookies at 3:45 in the Anderson Room, LN-2207.

Some meetings will be at other times, e.g., when joint with other seminars.

Tuesday, January 26
Organizational Meeting
Time: 1:15 - 1:45
Room: LN-2205

Friday, January 30 (Note special day)
Speaker: Lucas Rusnak (Binghamton)
Title: Multi-Directed Hypergraph Representations of {0, +1, −1}-Matrices
Time: 4:45 - 5:45 (Note special time)
Room: LN-2206 (Note special room)

Tuesday, February 3
Speaker: Lucas Sabalka (Binghamton)
Title: Projection-Forcing Multisets of Weight Changes
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, February 10
Speaker: Garry Bowlin (Binghamton)
Title: Maximum Frustration in Signed Complete Bipartite Graphs
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, February 24
Speaker: Laura Anderson (Binghamton)
Title: Face Enumeration in Simplicial Complexes
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, March 3
Speaker: Laura Anderson (Binghamton)
Title: f-Vectors of Barycentric Subdivisions
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, March 10
Speaker: Thomas Zaslavsky (Binghamton)
Title: Eight Queens and More
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, March 17
Speaker: Andy Fromader (Cornell)
Title: The Charney-Davis Conjecture for Certain Spheres
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, March 31
Speaker: Emanuele Delucchi (Binghamton)
Title: The 15 Puzzle on an Arbitrary Graph
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, April 14
Speaker: Luise-Charlotte Kappe (Binghamton)
Title: On the Covering Number of Symmetric and Alternating Groups: An Exercise in Combinatorial Optimization
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, April 28
Speaker: Louis Billera (Cornell)
Title: The Enumerative Combinatorial Geometry of Coxeter Groups
Time: 1:15 - 2:15
Room: LN-2205

Tuesday, May 5
Speaker: Christino Tamon (Clarkson)
Title: Mixing of Quantum Walks on Graphs
Time: 1:15 - 2:15
Room: LN-2205

Thursday, May 7
Speaker: Jackie Kaminski
Title: Flows on Graphs, and Related Topics: I
Time: 11:40 - 12:40
Room: LN-2201

Friday, May 8
Speaker: Jackie Kaminski
Title: Flows on Graphs, and Related Topics: II
Time: 10:50-11:50
Room: LN-2201

Tuesday, May 12 (Colloquium talk)
Speaker: Chris Godsil (Waterloo)
Title: Quantum Physics and Algebraic Graph Theory
Time: 1:20 - 2:20
Room: LN-2205
The possibility of a quantum computer has led to much new work in theoretical physics and, naturally enough, this work has raised many new mathematical problems. What is perhaps surprising is that it has led to interesting problems in algebraic graph theory. For example, questions about the relative power of a quantum computer lead to questions about the chromatic number of certain graphs. In my talk I will discuss some of these problems, and the progress that has been made.

Tuesday, May 12
Speaker: Chris Godsil (Waterloo)
Title: Erdös-Ko-Rado Theorems
Time: 4:30 - 5:30
Room: LN-2206
The Erdös-Ko-Rado Theorem tells us that if F is a collection of k-subsets of V = {1,...,v} such that any members of F have at least one point in common, then
1. |F| ≤ C(v-1, k-1).
2. If equality holds, then F consists of all k-subsets of V that contain some given point i of V.
This is certainly one of the central results in combinatorics. My aim in this talk is to introduce some of the many analogs of the EKR theorem, and to show how we can use linear algebra to prove them.