2019 Jun 03

Combinatorics - back to back:

11:00am to 1:00pm


CS Rothberg bldg, room B-500, Safra campus
First talk:
Speaker: Madeleine Weinstein (Berkeley)
Title: Voronoi Cells of Varieties
2019 May 27


11:00am to 1:00pm


CS Rothberg bldg, room B-500, Safra campus
Speaker: Uri Rabinovich (U. Haifa)
We shall discuss the following three issues:
* The existence of Hamiltonian d-cycles, i.e., simple d-cycles containing a spanning d-hypertree of a complete d-complex K_n^d;
* The existence of a distribution D over spanning d-hypertrees T of K_n^d, so that for ANY
(d-1)-cycle C there, the expected size of the d-filling of C with respect to a random T from D is Omega(n^d);
2019 Jun 24

Combinatorics: Doron Puder (TAU) "Aldous' spectral gap conjecture for normal sets"

11:00am to 1:00pm


CS bldg, room B-500, Safra campus
Speaker: Doron Puder, TAU
Title: Aldous' spectral gap conjecture for normal sets
Aldous' spectral gap conjecture, proved in 2009 by Caputo, Liggett and Richthammer, states the following a priori very surprising fact: the spectral gap of a random walk on a finite graph is equal to the spectral gap of the interchange process on the same graph.
2019 May 13

Combinatorics: Shira Zerbib (U. Michigan, Iowa State University) "Envy-free division of a cake without the “hungry players" assumption"

11:00am to 1:00pm


CS bldg, room B-500, Safra campus
Speaker: Shira Zerbib (U. Michigan, Iowa State University)
Title: Envy-free division of a cake without the “hungry players" assumption
The fair division theorem due to Stromquist (1980) ensures that under some conditions it is possible to divide a rectangular cake into n pieces and assign one piece to each of n players such that no player strictly prefers a piece that has not been assigned to him.
2019 May 06

Combinatorics: Omri Ben Eliezer (TAU) "Finding patterns in permutations"

11:00am to 1:00pm


CS building, room B-500, Safra campus
Speaker: Omri Ben Eliezer, TAU
Title: Finding patterns in permutations
For two permutations sigma and pi, we say that sigma contains a copy of
pi, if there is a subset (not necessarily consecutive) of elements in sigma,
whose relative order is the same as in pi. For example, if pi = (1,2,3),
then a copy of pi in sigma amounts to an increasing subsequence in sigma
of length 3.
As shown by Guillemot and Marx, a copy of a constant length pi can be
found in sigma in linear time. However, how quickly can one find such a
2019 May 27

NT & AG Seminar "A dream desingularization algorithm", Michael Temkin

2:30pm to 3:30pm

Abstract: Any birational geometer would agree that the best algorithm for resolution of singularities should run by defining a simple invariant of the singularity and iteratively blowing up its maximality locus. The only problem is that already the famous example of Whitney umbrella shows that this is impossible, and all methods following Hironaka had to use some history and resulted in more complicated algorithms. Nevertheless, in a recent work with Abramovich and Wlodarczyk we did construct such an algorithm, and an independent description of a similar
2019 May 21

Landau Lecture 3: Liftings mod p2 and the Nygaard filtration


Prof. Luc Illusie (Université Paris-Sud)
1:00pm to 2:00pm


Ross 70

Liftings mod p2 and the Nygaard filtration

Abstract: I will revisit old results on liftings mod p2 and decompositions of de Rham complexes in positive characteristic (Deligne-I.) at the light of relations recently discovered independently by Bhargav Bhatt and myself between cotangent complexes, de Rham-Witt, and derived de Rham complexes.

2019 Jun 20

Groups & dynamics seminar: Noam Kolodner (HUJI) - Surjectivity of morphisms of labeled core-graph under the action of automorphisms of a free group

10:00am to 11:00am

For a finitely generated subgroup H of the free group F_r, the Stallings graph of H is a finite combinatorial graph, whose edges are labeled by r letters (and their inverses), so that paths in the graphs correspond precisely to the words in H. Furthermore, there is a map between the graphs of two subgroups H and J, precisely when one is a subgroups of the other. Stallings theory studies the algebraic information which is encoded in the combinatorics of these graphs and maps.
2019 Jun 13

No seminar (IMU annual meeting)

10:00am to 11:10am

Abstract: A Markov chain over a finite state space is said to exhibit the total variation cutoff phenomenon if, starting from some Dirac measure, the total variation distance to the stationary distribution drops abruptly from near maximal to near zero. It is conjectured that simple random walks on the family of $k$-regular, transitive graphs with a two sided $\epsilon$ spectral gap exhibit total variation cutoff (for any fixed $k$ and $\epsilon). This is known to be true only in a small number of cases.