Seminars

2018 Jan 08

Combinatorics Seminar: Boris Lishak "The space of triangulations of a compact 4-manifold"

11:00am to 12:30pm

Location: 

Eilat Hall at IIAS
There are exponentially many triangulations of a fixed manifold extremely distant from each other in some natural metric. I will discuss similar results for contractible 2-complexes. In order to prove these for the manifold being the sphere (or a contractible complex) one needs to create topology out of nothing. This is done by studying group theory of the trivial group.
2017 Jan 09

Combinatorics: Ilan Karpas (HU) "Families with forbidden intersection patterns"

11:00am to 1:00pm

Location: 

Rothberg B220 (CS bldg)
Speaker: Ilan Karpas, HU Tilte: Families with forbidden intersection patterns Abstract: Let l, n be even natural numbers. A pattern p of length l is an element p = (p1, . . . , pl) ∈ {−, +}^l. Given such a pattern and two sets A, B ⊂ [n], we say that the pair (A, B) forms pattern p if the following conditions are satisfied: 1. A \Delta B = {i_1, . . . , i_l}, where i_1 < i_2 < . . . < i_l, 2. For 1 ≤ j ≤ l, we have i_ j ∈ A \ B if p_ j = + and i_ j ∈ B \ A if p_ j = −.
2016 Nov 07

László Babai (U. Chicago) "Finite permutation groups and the Graph Isomorphism problem"

10:40am to 12:50pm

Location: 

Israel Institute for Advanced Studies, Safra campus, Givat Ram
* This talk is joint with the 20th Midrasha Mathematicae: 60 faces to groups, celebrating Alex Lubotzky's 60th birthday. The full program for AlexFest, Nov. 6--11, is detailed here: http://www.as.huji.ac.il/ias/public/121/the20thMidrashaMa2016/program.pdf ----------- Speaker: László Babai (University of Chicago) Title: Finite permutation groups and the Graph Isomorphism problem Updated abstract: The Graph Isomorphism (GI) problem is the algorithmic problem
2017 Dec 18

Combinatorics seminar: Orit Raz

11:00am to 12:30pm

Location: 

Eilat Hal at IIAS
Title: Polynomials vanishing on Cartesian products Abstract: Let F(x,y,z) be a real trivariate polynomial of constant degree, and let A,B,C be three sets of real numbers, each of size n. How many roots can F have on A x B x C?
2017 Mar 20

Combinatorics: Doron Puder (TAU) "Meanders and Non-Crossing Partitions"

11:00am to 1:00pm

Location: 

Rothberg B220 (CS bldg)
Speaker: Doron Puder, TAU Title: Meanders and Non-Crossing Partitions Abstract: Imagine a long river and a closed (not self-intersecting) racetrack that crosses the river by bridges 2n times. This is called a meander. How many meanders are there with 2n bridges (up to homeomorphisms of the plane that stabilizes the river)? This challenging question, which is open for several decades now, has connections to several fields of mathematics.
2016 Dec 12

Combinatorics: Zur Luria (ETH)

11:00am to 1:00pm

Location: 

B220 Rothberg (CS)
Speaker: Zur Luria (ETH) Title: Hamiltonian spheres in random hypergraphs Abstract: Hamiltonian cycles are a fundamental object in graph theory, and combinatorics in general. A classical result states that in the random graph model G(n,p), there is a sharp threshold for the appearance of a Hamiltonian cycle. It is natural to wonder what happens in higher dimensions - that is, in random uniform hypergraphs?
2017 Nov 06

Combinatorics seminar: Eric Babson

11:00am to 12:30pm

Location: 

130 at the IIAS
Title: Gaussian Random Links Abstract: A model for random links is obtained by fixing an initial curve in some n-dimensional Euclidean space and projecting the curve on to random 3 dimensional subspaces. By varying the curve we obtain different models of random knots, and we will study how the second moment of the average crossing number change as a function of the initial curve. This is based on work of Christopher Westenberger.
2017 Feb 27

Combinatorics: Thilo Weinert (BGU) "The Ramsey Theory of ordinals and its relation to finitary combinatorics"

10:30am to 12:30pm

Location: 

Rothberg B220 (CS bldg)
Speaker: Thilo Weinert, BGU Title: The Ramsey Theory of ordinals and its relation to finitary combinatorics Abstract: Ramsey Theory is a branch of mathematics which is often times summed up by the slogan “complete disorder is impossible”. An important branch of finitary Ramsey Theory lies in the determination of Ramsey Numbers. Infinitary Ramsey Theory on the other hand is an important branch of set theory. Whereas the Ramsey Theory of the Uncountable often times features independence phenomena, the Ramsey Theory of the Countably Infinite provides many interesting combinatorial challenges.
2017 Jun 18

Combinatorics: Ehud Fridgut (Weizmann Institute) "Almost-intersecting families are almost intersecting-families."

11:00am to 1:00pm

Location: 

Rothberg B221 (CS building)
Speaker: Ehud Fridgut (Weizmann Institute) Title: Almost-intersecting families are almost intersecting-families. Abstract: Consider a family of subsets of size k from a ground set of size n (with k < n/2). Assume most (in some well defined sense) pairs of sets in the family intersect. Is it then possible to remove few (in some well defined sense) sets, and remain with a family where every two sets intersect? We will answer this affirmatively, and the route to the answer will pass through a removal lemma in product graphs.

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