2014
Jun
12

# Sasha Sodin

2:30pm to 3:30pm

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2014
Jun
12

2:30pm to 3:30pm

2014
Mar
20

2:30pm to 3:30pm

2015
Oct
22

2:30pm to 3:30pm

Title: Counting points and counting representations
Abstract:
I will talk about the following questions:
1) Given a system of polynomial equations with integer coefficients, how many solutions does it have in the ring Z/N?
2) Given a polynomial map f:R^a-->R^b and a smooth, compactly supported measure m on R^a, does the push-forward of m by f have bounded density?
3) Given a lattice in a higher rank Lie group (say, SL(n,Z) for n>2). How many d-dimensional representations does it have?

2014
May
22

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.

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.

2013
Dec
05

2:30pm to 3:30pm

2014
Jan
09

2:30pm to 3:30pm