Events & Seminars

2016 Nov 03

Groups and dynamics - Misha Belolipetsky

10:30am to 11:30am

Location: 

Ross 70
Speaker: Misha Belolipetsky
Title: Arithmetic Kleinian groups generated by elements of finite order
Abstract:
We show that up to commensurability there are only finitely many
cocompact arithmetic Kleinian groups generated by rotations. The proof
is based on a generalised Gromov-Guth inequality and bounds for the
hyperbolic and tube volumes of the quotient orbifolds. To estimate the
hyperbolic volume we take advantage of known results towards Lehmer's
problem. The tube volume estimate requires study of triangulations of
2017 May 25

Basic notions: Ehud de Shalit - The Loxton - van der Poorten conjecture

4:00pm to 5:00pm

Abstract: Adamczewski and Bell proved in the 2013 the Loxton - van der Poorten
conjecture. It says the following. Let f be a Laurent power series (with complex
coefficients) and let \sigma_p be the operator substituting x^p for x in f. Suppose that f satisfies a homogenous polynomial equation in the operator \sigma_p with
coefficients which are rational functions, and a similar equation in the operator \sigma_q where p and q are multiplicatively independent natural numbers. Then f is a rational function.
2017 May 18

Basic notions: Ehud de Shalit - The Loxton - van der Poorten conjecture

4:00pm to 5:00pm

Abstract: Adamczewski and Bell proved in the 2013 the Loxton - van der Poorten
conjecture. It says the following. Let f be a Laurent power series (with complex
coefficients) and let \sigma_p be the operator substituting x^p for x in f. Suppose that f satisfies a homogenous polynomial equation in the operator \sigma_p with
coefficients which are rational functions, and a similar equation in the operator \sigma_q where p and q are multiplicatively independent natural numbers. Then f is a rational function.
2017 Jun 11

Combinatorics: Ron Adin (BIU) "Cyclic descents, toric Schur functions and Gromov-Witten invariants"

11:00am to 1:00pm

Location: 

Rothberg B221 (CS building)
Speaker: Ron Adin (Bar-Ilan University)
Title: Cyclic descents, toric Schur functions and Gromov-Witten invariants
Abstract:
Descents of permutations have been studied for more than a century. This concept was vastly generalized, in particular to standard Young tableaux (SYT). More recently, cyclic descents of permutations were introduced by Cellini and further studied by Dilks, Petersen and Stembridge. Looking for a corresponding concept for SYT, Rhoades found a very elegant solution for rectangular shapes.
2015 Dec 03

Amitsur Algebra: Boris Plotkin (Hebrew U)

12:00pm to 1:15pm

Location: 

Manchester Building (room 209), Jerusalem, Israel
Title: Algebraic Geometry in an arbitrary variety of algebras and Algebraic Logic
Abstract: I will speak about a system of notions which lead to interesting new problems for groups and algebras as well as to reinterpretation of some old ones.
2015 Dec 24

Amitsur Algebra: Michael Larsen (Indiana U)

12:00pm to 1:15pm

Location: 

Manchester Building (room 209), Jerusalem, Israel
Title: Character values on compact simple Lie groups
Abstract: This work is part of a joint project with Aner and others to find upper bounds for values of irreducible characters in two related settings: compact simple Lie groups and finite groups of Lie type. I will discuss the first case, presenting bounds of the form
$$|\chi(g)| = O(\chi(1)^\alpha),$$
2016 Mar 29

Dynamics & probability: Paul Nelson (ETH) - Microlocal lifts and quantum unique ergodicity on GL(2,Q_p)

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Abstract:
There are by now several celebrated measure classification results to the effect that a measure is uniform provided it possesses sufficient "invariance" as quantified by stabilizer, entropy, or recurrence. In some applications, part of the challenge is to identify or construct measures to which these hypotheses apply.
2018 Jan 15

Michael Farber: "Robot motion planning and equivariant Bredon cohomology"

9:00am to 11:00am

Location: 

IIAS, Feldman Building, Givat Ram

Abstract: The motion planning problem of robotics leads to an interesting invariant of topological spaces, TC(X), depending on the homotopy type of X = the configuration space of the system. TC(X) is an integer reflecting the complexity of motion planning algorithms for all systems (robots) having X as their configuration space. Methods of algebraic topology allow to compute or to estimate TC(X) in many examples of practical interest. In the case when the space X is aspherical the number TC(X) depends only on the fundamental group of X.

2018 Mar 05

HD-Combinatorics Special Day: Samplers in Computer Science (organized by Amnon Ta-Shma)

(All day)

Location: 

Room 130, IIAS, Feldman Building, Givat Ram

All talks will be given by Amnon Ta-Shma.
10:00-11:00 - The sampling problem and some equivalent formulations

11:30-12:30 - A basic "combinatorial" construction

14:00-14:45 - Algebraic constructions of randomness condensers

15:15-16:00 - Structured sampling

Program:

1. 10:00-11:00 - The sampling problem and some equivalent formulations. 
Abstract:
We will first define Samplers, and the parameters that
one usually tries to optimize: accuracy, confidence, query complexity
2018 Mar 22

Colloquium: Gilles Zemor (Université de Bordeaux) - "Additive Combinatorics in Field Extensions"

3:30pm to 4:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Additive combinatorics enable one to characterize subsets S of elements in a group such that S+S has small cardinality. We are interested in linear analogues of these results, namely characterizing subspaces S in some algebras (mostly extension fields) such that the linear span of the set S^2 of products st, for s,t in S, has small dimension. We shall present a linear analogue of a theorem of Vosper which says that under the right conditions, a sufficiently small dimension for S^2 implies that S has a basis of elements in geometric progression.

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