2018
Jun
21

# No Basic notions seminar - deferred to 25.6

4:00pm to 4:00am

2018
Jun
21

4:00pm to 4:00am

2018
Jun
14

4:00pm to 5:15pm

Ross 70

Ergodic theoretic methods in the context of homogeneous dynamics have been highly successful in number theoretic and other applications. A lacuna of these methods is that usually they do not give rates or effective estimates. Einseidler, Venkatesh and Margulis proved a rather remarkable quantitative equidistribution result for periodic orbits of semisimple groups in homogenous spaces that can be viewed as an effective version of a result of Mozes and Shah based on Ratner's measure classification theorem.

2018
Jun
25

4:30pm to 5:45pm

This is the second of two lectures on the paper Einseidler,, Margulis, Mohammadi and Venkatesh https://arxiv.org/abs/1503.05884. In this second lecture I will explain how the authors obtain using property tau (uniform spectral gap for arithmetic quotient) quantitaive equidistribution results for periodic orbits of maximal semisimple groups. Surprisingly, one can then use this theorem to establish property tau...

2018
Dec
12

Igor Pak (UCLA)

10:30am to 12:00pm

Rothberg (CS building) B-220

Contingency tables are matrices with fixed row and column sums. They are in natural correspondence with bipartite multi-graphs with fixed degrees and can also be viewed as integer points in transportation polytopes. Counting and random sampling of contingency tables is a fundamental problem in statistics which remains unresolved in full generality.

In the talk, I will review both asymptotic and MCMC approaches, and then present a new Markov chain construction which provably works for sparse margins. I conclude with some curious experimental results and conjectures. Read more about CS Theory -- Erdős Lecture II: Counting contigency tables

2019
May
01

12:00pm to 1:00pm

Ross 70

Title: On tiling the real line by translates of a function

Abstract: If f is a function on the real line, then a system

of translates of f is said to be a << tiling >> if it constitutes

a partition of unity. Which functions can tile the line by

translations, and what can be said about the structure of the

tiling? I will give some background on the problem and present

our results obtained in joint work with Mihail Kolountzakis.

Abstract: If f is a function on the real line, then a system

of translates of f is said to be a << tiling >> if it constitutes

a partition of unity. Which functions can tile the line by

translations, and what can be said about the structure of the

tiling? I will give some background on the problem and present

our results obtained in joint work with Mihail Kolountzakis.

2018
Jun
12

1:00pm to 2:30pm

Room 110, Manchester Buildling, Jerusalem, Israel

Open Gromov-Witten (OGW) invariants count pseudoholomorphic maps from a Riemann surface with boundary to a symplectic manifold, with constraints that make sure the moduli space of solutions is zero dimensional. In joint work with J. Solomon (2016-2017), we defined OGW invariants in genus zero under cohomological conditions. In this talk, also based on joint work with J. Solomon, I will describe a family of PDEs satisfied by the generating function of our invariants. We call this family the open WDVV equations.

2018
Jun
11

10:00am to 10:50am

Feldman Building, Givat Ram

In the past decades There has been considerable interest in the probability that two random elements of (finite or certain infinite)

groups commute.

I will describe new works (by myself and by others) on probabilistically nilpotent groups, namely groups in which the probability that [x_1,...,x_k]=1 is positive/bounded away from zero.

It turns out that, under some natural conditions,

these are exactly the groups which have a finite/bounded index

subgroup which is nilpotent of class < k.

The proofs have some combinatorial flavor.

groups commute.

I will describe new works (by myself and by others) on probabilistically nilpotent groups, namely groups in which the probability that [x_1,...,x_k]=1 is positive/bounded away from zero.

It turns out that, under some natural conditions,

these are exactly the groups which have a finite/bounded index

subgroup which is nilpotent of class < k.

The proofs have some combinatorial flavor.

2018
Jun
11

9:00am to 9:50am

Feldman Building, Givat Ram

Let X be the spherical building associated to the group G=GL(n,F) ,

where F is a finite field. We will survey some results on the homology of X with constant and twisted coefficients, and on the corresponding expansion properties.

where F is a finite field. We will survey some results on the homology of X with constant and twisted coefficients, and on the corresponding expansion properties.

2018
Jun
11

2:00pm to 3:50pm

Feldman Building, Givat Ram

In this talk we recall Conlon's random construction of sparse 2-dim simplicial complexes arising from Cayley graphs of F_2^t . We check what expansion properties this construction has (and doesn't have): Mixing of random walks, Spectral gap of the 1-skeleton, Spectral gap of the links, Co-systolic expansion and the geometric overlap property.

2018
Jun
04

10:00am to 10:50am

Feldman Building, Givat Ram

Locally testable codes are error-correcting codes that admit

super-efficient checking procedures. In the first part of the talk, we will

see why expander based codes are NOT locally testable. This is in contrast

to typical "good" error correcting properties which follow from expansion.

We will then see that despite this disconnect between expansion and

testability, all known construction of locally testable codes follow from

the high-dimensional expansion property of a related complex leaving open

super-efficient checking procedures. In the first part of the talk, we will

see why expander based codes are NOT locally testable. This is in contrast

to typical "good" error correcting properties which follow from expansion.

We will then see that despite this disconnect between expansion and

testability, all known construction of locally testable codes follow from

the high-dimensional expansion property of a related complex leaving open

2018
Jun
04

9:00am to 9:50am

Feldman Building, Givat Ram

Computing R=P.Q ,the product of two mXm Boolean matrices [BMM] is an ingredient

of many combinatorial algorithms.

Many efforts were made to speed it beyond the standard m^3 steps, without using

the algebraic multiplication.

To divide the computation task, encoding of the rows and column indices were

used (1.1) j by (j1,j2) k by (k1,k2)

e.g. using integer p j2=j mod p ,j1=ceiling of j/p.

Clearly, the product of the ranges of the digits= m1.m2 - is approximately m.

2018
Jun
04

2:00pm to 3:50pm

Feldman Building, Givat Ram

In this talk we shall review a paper by Gromov and Guth, in which they introduced several ways to measure the geometric complexity of an embedding of simplicial complexes to Euclidean spaces.

One such measurement is strongly related to the notion of high dimensional expanders introduced by Gromov, and in fact, it is based on a paper of Kolmogorov and Barzadin from 1967, in which the notion of an expander graph appeared implicitly.

We shall show one application of bounded degree high dimensional expanders, and present many more open questions arising from the above mentioned paper.

One such measurement is strongly related to the notion of high dimensional expanders introduced by Gromov, and in fact, it is based on a paper of Kolmogorov and Barzadin from 1967, in which the notion of an expander graph appeared implicitly.

We shall show one application of bounded degree high dimensional expanders, and present many more open questions arising from the above mentioned paper.

2018
May
29

1:30pm to 3:00pm

The set of real numbers is often identified with

Cantor Space 2^omega, with which it shares many important

properties: not only the cardinality, but also other

"cardinal characteristics" such as cov(null), the smallest

number of measure zero sets needed to cover the whole space,

and similarly cov(meager), where meager="first category";

or their "dual" versions non(meager) (the smallest

cardinality of a nonmeager set) and non(null).

Many ZFC results and consistency results (such as

Cantor Space 2^omega, with which it shares many important

properties: not only the cardinality, but also other

"cardinal characteristics" such as cov(null), the smallest

number of measure zero sets needed to cover the whole space,

and similarly cov(meager), where meager="first category";

or their "dual" versions non(meager) (the smallest

cardinality of a nonmeager set) and non(null).

Many ZFC results and consistency results (such as

2018
Jun
26

2:15pm to 3:15pm

Suppose that a countable group $G$ acts on a compact metric space $X$ and that $S \subset G$ is a semigroup not containing the identity of $G$. If every continuous function $f$ on $X$ is contained in the closed algebra generated by $\{sf : s \in S\}$, the action is said to be $S$-predictable.

In this talk, we consider the following question due to Hochman:

When $G$ is amenable, does $S$-predictability imply zero topological entropy?

To provide an affirmative answer, we introduce the notion of a random invariant order.

In this talk, we consider the following question due to Hochman:

When $G$ is amenable, does $S$-predictability imply zero topological entropy?

To provide an affirmative answer, we introduce the notion of a random invariant order.

2018
May
28

(All day)

Eilat Hall, Feldman Building, Givat Ram

09:00 - 10:50 **Noga Ron-Zewi**, "Locally testable codes"

14:00 - 14:50**Dorit Aharonov**, "Quantum error correcting codes"

15:00 - 15:50**Dorit Aharonov**, " Quantum Locally Testable codes and High dimensional expansion"

Abstract for Noga Ron-Zewi's talk:

14:00 - 14:50

15:00 - 15:50

Abstract for Noga Ron-Zewi's talk: