2014
Jan
16

# Peter Sarnak

2:30pm to 3:30pm

2014
Jan
16

2:30pm to 3:30pm

2014
Feb
27

2:30pm to 3:30pm

2013
Nov
14

2:30pm to 3:30pm

2013
Dec
26

2:30pm to 3:30pm

2014
May
01

2:30pm to 3:30pm

2017
Jan
22

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.

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.

2013
Nov
28

2:30pm to 3:30pm

2014
Mar
27

2:30pm to 3:30pm

2015
Oct
29

2:30pm to 3:30pm

Title: Avatars of small cancellation

Abstract:

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.

Abstract:

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.

2013
Dec
05

2:30pm to 3:30pm

2014
Jan
09

2:30pm to 3:30pm

2017
Sep
14

2:30pm to 3:30pm

IIAS hall, Hebrew University Jerusalem

I will give introduction to sofic groups and discuss a possible strategy towards finding a non-sofic group. I will show that if the Higman group were sofic, there would be a map from Z/pZ to itself, locally like an exponential map, satisfying a rather strong recurrence property. The approach to (non)-soficity is based on the study of sofic representations of amenable subgroups of a sofic group. This is joint work with Harald Helfgott.

2016
Jan
10

4:00pm to 5:00pm

Ross 70A

Abstract: The original construction uses the theory of pseudo-holomorphic curves. In this lecture, I will describe an explicit combinatorial algorithm for computing knot Floer homology in terms of grid diagrams. In this lecture, I will describe joint work with Ciprian Manolescu, Sucharit Sarkar, Zoltan Szabo, and Dylan Thurston.

2017
May
23

1:00pm to 1:50pm

Ross A70.

Abstract: Let \Sigma be a compact connected oriented 2-manifold of genus g , and let p be a point on \Sigma. We define a space S_g(t) consisting of certain irreducible representations of the fundamental group of \Sigma - { p } , modulo conjugation by SU(N).

2017
Aug
09

12:00pm to 1:00pm

Room 70A, Ross Building, Jerusalem, Israel

Knot Floer homology is an invariant for knots in the three-sphere defined using methods from symplectic geometry. I will describe a new algebraic formulation of this invariant which leads to a reasonably efficient computation of these invariants. This is joint work with Zoltan Szabo.