Eventss

2019 May 13

NT & AG Seminar: "A dream desingularization algorithm", Michael Temkin (HU)

2:30pm to 4:00pm

Location: 

Ross 70
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 07

Anatoly Vershik (St. Petersburg) Соmbinatorial (locally finite) еncoding of the Bernoulli processes with infinite entropy.

2:00pm to 3:00pm

Abstract. The realization of m.p automorphisms as transfer on the space of the paths on the graded graphs allows to use new kind of encoding of one-sided Bernoulli shift. I will start with simple example how to realize Bernoulli shift in the locally finite space (graph) $\prod_n {1,2,\dots n}$ (triangle compact.) Much more complicated example connected to old papers by S.Kerov-Vershik and recent by Romik-Sniady in which one-sided Bernoulli shift is realized as Schutzenberger transfer on the space of infinite Young tableaux with Plancherel Measure. These examples open series of
2019 Jun 27

Group and dynamics seminar: Michael Chapman (HUJI): Cutoff on Ramanujan complexes

10:00am to 11:15am

Location: 

Ross 70
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.
2019 Jun 03

Combinatorics - back to back:

11:00am to 1:00pm

Location: 

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

Combinatorics: Uri Rabinovich (U. Haifa) "SOME EXTREMAL PROBLEMS ABOUT SIMPLICIAL COMPLEXES"

11:00am to 1:00pm

Location: 

CS Rothberg bldg, room B-500, Safra campus
Speaker: Uri Rabinovich (U. Haifa) Title: SOME EXTREMAL PROBLEMS ABOUT SIMPLICIAL COMPLEXES Abstract: 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); * The existence of f(k,d) such that any d-simplex of rank r with > f(k,d)*r d-faces contains
2019 Jun 24

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

11:00am to 1:00pm

Location: 

CS bldg, room B-500, Safra campus
Speaker: Doron Puder, TAU Title: Aldous' spectral gap conjecture for normal sets Abstract: 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

Location: 

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 Abstract: 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

Location: 

CS building, room B-500, Safra campus
Speaker: Omri Ben Eliezer, TAU Title: Finding patterns in permutations Abstract: 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

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