2017 Jan 22

Special colloquium: Laci Babai (Chicago) "Graph isomorphism and coherent configurations: The Split-or-Johnson routine"

4:00pm to 6:00pm


Rothberg B220 (CS bldg)
Coherent configurations" (CCs) are certain highly regular colorings of the directed complete graph. The concept goes back to Schur (1933) who used it to study permutation groups, and has subsequently been rediscovered in other contexts (block designs,
association schemes, graph canonization).
CCs are the central concept in the "Split-or-Johnson" (SoJ) procedure, one of the main combinatorial components of the speaker's recent algorithm to test graph isomorphism.
2015 Oct 29

Colloquium: Vincent Guirardel (Universite de Renne 1), "Avatars of small cancellation"

2:30pm to 3:30pm

Title: Avatars of small cancellation
In general, given a finite presentation of a group, it is very difficult (in fact algorithmically impossible) to understand the group it defines. Small cancellation theory was developped as a combinatorial condition on a presentation that allows one to understand the group it represents. This very flexible construction has many applications to construct examples of groups with specific features.
2017 Jun 08

Wolf Prize Lecture - Rick Schoen (Stanford): The geometry of eigenvalue extremal problems

11:00am to 12:00pm


Levin building, lecture hall 8
Title: “The geometry of eigenvalue extremal problems”
Abstract: When we choose a metric on a manifold we determine the spectrum of
the Laplace operator. Thus an eigenvalue may be considered as a functional
on the space of metrics. For example the first eigenvalue would be the fundamental
vibrational frequency. In some cases the normalized eigenvalues are bounded
independent of the metric. In such cases it makes sense to attempt to find
critical points in the space of metrics. In this talk we will survey two cases in