Skip to main content
Department of Mathematics

Purdue Topology Seminar

In Spring 2026, the Purdue Topology Seminar will be held on Wednesdays 10:20am - 11:20am Eastern time in DSAI 1004 (when we meet in person) unless otherwise noted.  If you want to be added to our email list please contact Shawn Cui (shawn.cui at purdue.edu) or Manuel Rivera (manuelr at purdue.edu). 

Some recorded talks may be found on our YouTube Channel.

 

Spring 2026

January 14 (in-person)

Eric Samperton (Purdue)

Title: Obstruction theory and counting complexity

Abstract: For a fixed finite group G, I will explain what it is known about how hard it is to count group homomorphisms from another group Γ to G.  To make things precise, one must specify how Γ is encoded.  On one hand, if Γ is a finitely presented group, then the counting problem is #P-hard as soon as G is non-abelian.  This follows as an easy corollary of major results of Bulatov and Dalmau on the computational complexity of counting CSPs (constraint satisfaction problems).  On the other hand, if G is class 2 nilpotent and Γ is either a finite group provided via a multiplication table or the fundamental group of a triangulated 3-manifold, then there exist efficient algorithms to compute this count.  The tension between the two theorems is resolved by understanding how easy/hard it is to access a triangulation of the three skeleton of the Eilenberg-MacLane space K(Γ, 1) from the given encoding of Γ.

I will introduce all of the complexity theory necessary, and I will also give some motivations coming from topological quantum computing.  This talk is based on joint work with Armin Weiss.

 

February 3 (in-person)

Department Colloquium, Tuesday 3:00-4:00 pm in Math 175

Hiro Lee Tanaka (Texas State University)

 

February 11 (in-person) 

Pierre Godfard (University of North Carolina)

 

February 18 (online) 

Nicolas Guès (Paris 13)

 

March 5 (in-person, note this is a Thursday) 

Jennifer Wilson (University of Michigan)

 

March 11 (in-person) 

Peter Patzt (University of Oklahoma)

 

Purdue topology group:

Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, IN 47907-2067

Phone: (765) 494-1901 - FAX: (765) 494-0548  Contact Us

© 2025 Purdue University | An equal access/equal opportunity university | Copyright Complaints | DOE Degree Scorecards | Accessibility