Seminars

2016 Feb 22

Combinatorics

Repeats every week every Monday until Sun Feb 28 2016 .
10:30am to 12:30pm

Location: 

B221 Rothberg (CS and Engineering building)
Speaker: Asaf Nachmias (TAU) Title: The connectivity of the uniform spanning forest on planar graphs Abstract: The free uniform spanning forest (FUSF) of an infinite connected graph G is obtained as the weak limit uniformly chosen spanning trees of finite subgraphs of G. It is easy to see that the FUSF is supported on spanning graphs of G with no cycles, but it need not be connected. Indeed, a classical result of Pemantle ('91) asserts that when G=Z^d, the FUSF is almost surely a connected tree if and only if d=1,2,3,4.
2015 Nov 09

Combinatorics seminar

Repeats every week every Monday until Mon Nov 23 2015 .
11:00am to 1:00pm

11:00am to 1:00pm

Location: 

B221 Rothberg (CS and Engineering building)
Speaker: Clara Shikhelman, TAU Title: Many T copies in H-free graphs. Abstract: For two graphs T and H and for an integer n, let ex(n,T,H) denote the maximum possible number of copies of T in an H-free graph on n vertices. The study of this function when T=K_2 (a single edge) is the main subject of extremal graph theory. We investigate the general function, focusing on the cases of triangles, complete graphs and trees. In this talk the main results will be presented as will sketches of proofs of some of the following: (i) ex(n,K_3,C_5) < (1+o(1)) (\sqrt 3)/2 n^{3/2}.
2015 Nov 19

Special Combinatorics seminar: Horst Martini (TU Chemnitz, Germany), "Discrete Geometry in Minkowski Spaces"

12:00pm to 1:00pm

Location: 

Rothberg B314
Title: Discrete Geometry in Minkowski Spaces Abstract: In recent decades, many papers appeared in which typical problems of Discrete Geometry are investigated, but referring to the more general setting of finite dimensional real Banach spaces (i.e., to Minkowski Geometry). In several cases such problems are investigated in the even more general context of spaces with so-called asymmetric norms (gauges). In many cases the extension of basic geometric notions, needed for posing these problems in non-Euclidean Banach spaces, is already interesting enough.
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?

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