2018
Jan
01

# Combinatorics Seminar: Raphael Yuster

11:00am to 12:30pm

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2018
Jan
01

11:00am to 12:30pm

2017
May
07

11:00am to 1:00pm

2016
Nov
07

10:40am to 12:50pm

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

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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

The full program for AlexFest, Nov. 6--11, is detailed here:

http://www.as.huji.ac.il/ias/public/121/the20thMidrashaMa2016/program.pdf

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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

11:00am to 12:30pm

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
Jan
02

11:00am to 1:00pm

Rothberg B220 (CS)

Speaker: Ron Holzman, Technion

Title: Edge-covers in d-interval hypergraphs

Title: Edge-covers in d-interval hypergraphs

2018
Jan
22

11:00am to 12:30pm

Room 130, Feldman Building

Title: Shellability is NP-complete

2017
Mar
20

11:00am to 1:00pm

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.

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
Jun
16

11:00am to 12:00pm

Rothberg A410

Speaker: Bram Petri, Max Planck Institute, Bonn

Title: The length spectrum of a random surface

Title: The length spectrum of a random surface

2017
Nov
13

11:00am to 12:30pm

2016
Dec
12

11:00am to 1:00pm

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?

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

11:00am to 12:30pm

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.

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

10:30am to 12:30pm

Rothberg B220 (CS bldg)

Speaker: Thilo Weinert, BGU

Title: The Ramsey Theory of ordinals and its relation to finitary combinatorics

Abstract:

Title: The Ramsey Theory of ordinals and its relation to finitary combinatorics

Abstract:

2017
Jun
18

11:00am to 1:00pm

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.

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.

2016
Nov
28

11:00am to 1:00pm

B220 Rothberg (CS building)

Speaker: Elon Lindenstrauss (HU)

Title: On the spectral gap of Cayley graphs for the group of affine transformations

Abstract: Joint work with P. Varju.

One of the most important open questions regarding spectral gap of Cayley graphs is the dependence of the gap on the choice of generators.

Title: On the spectral gap of Cayley graphs for the group of affine transformations

Abstract: Joint work with P. Varju.

One of the most important open questions regarding spectral gap of Cayley graphs is the dependence of the gap on the choice of generators.

2017
Dec
04

11:00am to 12:30pm

Room 130 IIAS

Title:

The Theta Number of Simplicial Complexes

Abstract:

The celebrated Lovász theta number of a graph is an efficiently computable upper bound for the independence number of a graph, given by a semidefinite program. This talk presents a generalization of the theta number to simplicial complexes of arbitrary dimension, based on real simplicial cohomology theory, in particular higher dimensional Laplacians.

The Theta Number of Simplicial Complexes

Abstract:

The celebrated Lovász theta number of a graph is an efficiently computable upper bound for the independence number of a graph, given by a semidefinite program. This talk presents a generalization of the theta number to simplicial complexes of arbitrary dimension, based on real simplicial cohomology theory, in particular higher dimensional Laplacians.