[Binghamton Geometry/Topology Seminar] Topological Properties of Activity Orders for Matroid Bases

[Dikran B. Karagueuzian]

The following talk will be of interest to many topologists.
Apologies to those on both the topology and combinatorics
mailing lists, who have received this announcement twice.


			COMBINATORICS SEMINAR

			 Friday, February 6


Speaker: Bruce Sagan (Michigan State)
Title: Topological Properties of Activity Orders for Matroid Bases
Time: 3:30 - 4:30 	(Note the time.)
Room: LN-2205 		(Note the room.)

			      Abstract

Las Vergnas recently defined partial orders on the bases of an ordered 
matroid using their internal and external activities. He showed that 
these 
posets are in fact graded lattices. We study the order complex of 
these 
lattices, showing that it is always homotopy equivalent to a shellable 
complex. This helps explain an observation of Las Vergnas, that the 
Mobius 
function of these lattices is often zero.

I will not assume any background about matroids or topology of posets.

This is joint work with Rieuwert Blok. 

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The seminar's Web page is
	http://www.math.binghamton.edu/dept/ComboSem/index.html