====== The Combinatorics Seminar ====== ===== FALL 2008 ===== [[http://www.anybrowser.org/campaign/|Best Viewed With Any Browser]] [[http://www.math.binghamton.edu/dept/directions.html|Directions to the department.]] Organizers: [[delucchi/|Emanuele Delucchi]], and [[zaslav/|Thomas Zaslavsky]]. 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. ---- This semester we will have several talks on **non-crossing partitions**. Here is the link to a [[nc-partitions-bibliography.2008.html|short bibliography]], including papers that will be presented. Here are links to a [[nc-partitions.mr1.pdf|first list]] and [[nc-partitions.mr2.pdf|second list]] of relevant papers with reviews (there is overlap with the short bibliography).

**Tuesday, September 2**\\ Organizational Meeting (all should come)\\ + chat with\\ //Speaker//: Thomas Zaslavsky (Binghamton)\\ //Title//: [[abstract.200809zas|Fun at Summer Conferences]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, September 9**\\ //Speaker//: Emanuele Delucchi (Binghamton)\\ //Title//: [[abstract.200809del|Finite Reflection Groups, Non-Crossing Partitions, and a Theorem of Deligne]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, September 16**\\ //Speaker//: Thomas Zaslavsky (Binghamton)\\ //Title//: [[abstract.200809zasa|Quasigroups via Graphs]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, September 23**\\ //Speaker//: Ed Swartz (Cornell)\\ //Title//: [[abstract.200809swa|Three Complexes]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, September 30**\\ Holiday; no meeting.
**Tuesday, October 7**\\ //Speaker//: Thomas Zaslavsky (Binghamton)\\ //Title//: [[abstract.200810zas|Tutte Functions of Matroids]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, October 14**\\ //Speaker//: Garry Bowlin (Binghamton)\\ //Title//: [[abstract.200810bow|Non-Crossing Partitions, I]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, October 21**\\ //Speaker//: Garry Bowlin (Binghamton)\\ //Title//: [[abstract.200810bow|Non-Crossing Partitions, II]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Wednesday, October 29 (Special day)**\\ //Speaker//: Laura Anderson (Binghamton)\\ //Title//: [[abstract.200810and|Representation of Matroids by Homotopy Spheres]]\\ //Time//: 2:20 - 3:20 **(Special time)**\\ //Room//: LN-2205
**Tuesday, November 4**\\ //No meeting today – Election day.//
**Tuesday, November 11**\\ //Speaker//: Nate Reff (Binghamton)\\ //Title//: [[abstract.200811ref|The Lattice of Non-Crossing Partitions]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Thursday, November 13 ([[../colloquia/|Colloquium]])**\\ //Speaker//: Joanna Ellis-Monaghan (St. Michael's College)\\ //Title//: [[abstract.200811ellc|The Tutte Polynomial and Potts Model in Statistical Mechanics]]\\ //Time//: 4:30 - 5:30\\ //Room//: LN-2205
**Friday, November 14 (Special day)**\\ //Speaker//: Joanna Ellis-Monaghan (St. Michael's College)\\ //Title//: [[abstract.200811ells|Multivariable Tutte and Transition Polynomials]]\\ //Time//: 2:20 - 3:20 **(Special time)**\\ //Room//: LN-2205
**Tuesday, November 18**\\ //Speaker//: Jackie Kaminski (Binghamton)\\ //Title//: [[abstract.200811kam|Regular Non-Crossing Partitions]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, November 25 (joint with the [[../AlgebraSem/index.html|Algebra Seminar]])**\\ //Speaker//: Thomas Zaslavsky (Binghamton)\\ //Title//: [[abstract.200811zas|Graphic Matrices Over a Group]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205
**Tuesday, December 2 (joint with the [[../AlgebraSem/index.html|Algebra Seminar]])**\\ //Speaker//: Simon Joyce (Binghamton)\\ //Title//: [[abstract.200812joy|The Symmetric Group and Non-Crossing Partitions]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205

I will define a poset relation on the symmetric group S_n, which gives a natural order-preserving function from S_n to the lattice of partitions. If we restrict our attention to elements in S_n under a particular n-cycle, we have a lattice which is isomorphic to the lattice of non-crossing partitions. If time permits I'll talk about some of the implications. This work is based on a paper by Thomas Brady.
**Tuesday, December 9**\\ //Speaker//: Lucas Rusnak (Binghamton)\\ //Title//: [[abstract.200812rus|A Multidirected Hypergraph Representation of Matrices with 0, 1, −1 Entries, Part I]]\\ //Time//: 1:15 - 2:15\\ //Room//: LN-2205

A multi-directed hypergraph is a combinatorial representation of {0, +1, −1}-matrices that extends the concepts of signed graphs to hypergraphic analogs. I will discuss their discovery and development from hypergraphic matrices and the problems in extending the signed-graphic treatment of the classification of column dependencies.
**Tuesday, December 16**\\ //Speaker//: Lucas Rusnak (Binghamton)\\ //Title//: [[abstract.200812rus|A Multidirected Hypergraph Representation of Matrices with 0, 1, −1 Entries, Part II]]\\ //Time//: 2:50 - 3:50 **(Special time)**\\ //Room//: SW-231 **(Special room)**

A multi-directed hypergraph is a combinatorial representation of {0, +1, −1}-matrices that extends the concepts of signed graphs to hypergraphic analogs. I will discuss their discovery and development from hypergraphic matrices and the problems in extending the signed-graphic treatment of the classification of column dependencies.

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