Events & Seminars

2019 Mar 19

Dynamics Seminar: Elon Lindenstrauss (HUJI) - Double variational principle for mean dimension

2:15pm to 3:15pm

Mean dimension is a topological invariant of dynamical systems introduced by Gromov that measures the number of parameters per iteration needed to describe a trajectory in the system. We characterize this invariant (at least for dynamical systems with the marker property, such as infinite minimal systems) using a min-max principle, where choices of both a metric on the topological space and an invariant probability measure on the system are varied.
The work I will report on is joint work with M. Tsukamoto.
2019 Jan 15

T&G: Michael Khanevsky (Technion), Geometry of sets of Hamiltonian isotopic curves in a symplectic surface

2:00pm to 3:30pm

Location: 

Room 209, Manchester Building, Jerusalem, Israel

Given two Hamiltonian isotopic curves in a surface, one would like to tell whether they are "close" or "far apart". A natural way to do that is to consider Hofer's metric which computes mechanical energy needed to deform one curve into the other. However due to lack of tools the large-scale Hofer geometry is only partially understood. On some surfaces (e.g. S^2) literally nothing is known.
2019 May 15

Analysis Seminar: Matthias Keller (Potsdam) "Path integral representations for magnetic Schroedinger operators on graphs"

12:00pm to 1:00pm

Location: 

Ross 70

Title:
Path integral representations for magnetic Schroedinger operators on graphs
Abstract:
We consider the semigroup and the unitary group of magnetic Schrödinger operators on graphs. Using the ideas of the Feynman Kac formula, we develop a representation of the semigroup and the unitary group in terms of the stochastic process associated with the free Laplacian. As a consequence we derive Kato-Simon estimates for the unitary group. This is joint work with Batu Güneysu (Bonn).
2019 Apr 02

Dynamics Seminar : Yonatan Gutman (IMPAN). On Almost Lossless Compression

2:15pm to 3:15pm

Location: 

Ross 70
Abstract: We answer the following questions:
1. Consider a Borel set $X \subset \R^N$ equipped with a probability measure $\mu$. For fixed $k 2. Can one prove a probabilistic version of Takens delay-embedding theorem with less observations?
3. Is metric mean dimension related to analog compression?
Based on joint works with Krzysztof Barański and Adam Śpiewak.
2019 Jan 09

Set Theory Seminar - Ur Yaar (Set Theory Seminar - Ur Yaar Set Theory Seminar - Ur Yaar Set Theory Seminar - Ur Yaar Set Theory Seminar - Ur Yaar Set Theory Seminar - Ur Yaar )Set Theory Seminar - Ur Yaar Set Theory Seminar - Ur Yaar

2:00pm to 3:30pm

Location: 

Ross 73
Title: The Modal Logic of Forcing (Part III)
Abstract: Modal logic is used to study various modalities, i.e. various ways in which statements can be true, the most notable of which are the modalities of necessity and possibility. In set-theory, a natural interpretation is to consider a statement as necessary if it holds in any forcing extension of the world, and possible if it holds in some forcing extension. One can now ask what are the modal principles which captures this interpretation, or in other words - what is the "Modal Logic of Forcing"?
2019 Apr 30

Dynamics Lunch: Nishant Chandgotia "Generic properties of Lebesgue measure preserving transformations of the 2-torus."

12:00pm to 1:00pm


Abstract: In this talk we will discuss some recent work by Guihéneuf and Lefeuvre who prove that shadowing is generic for Lebesgue measure preserving transformations of the 2-torus. We will spend most of our time motivating the problem, discussing the history of such questions- specifically touching upon earlier work of Oxtoby, Ulam, Alpern and Prasad and some general techniques used in the area. Time permitting, we will discuss the recent proof given by Guihéneuf and Lefeuvre.
2019 Jan 08

T&G: David Treumann (Boston College), The Fargues-Fontaine curve for symplectic geometers -- NOTE special time and location

4:00pm to 5:30pm

Location: 

Room 70, Ross Building, Jerusalem, Israel
I will review homological mirror symmetry for the torus, which describes Lagrangian Floer theory on T^2 in terms of vector bundles on the Tate elliptic curve --- a version of Lekili and Perutz's works "over Z", where t is the Novikov parameter. Then I will describe a modified form of this story, joint with Lekili, where the Floer theory is altered by a locally constant sheaf of rings on T^2 (an "F-field").
2019 Feb 20

Analysis Seminar: Itay Londner (UBC) "Interpolation sets and arithmetic progressions"

12:00pm to 1:00pm

Location: 

Ross 70
Title: Interpolation sets and arithmetic progressions
Abstract: Given a set S of positive measure on the unit circle, a set of integers K is an interpolation set (IS) for S if for any data {c(k)} in l^2(K) there exists a function f in L^2(S) such that its Fourier coefficients satisfy f^(k)=c(k) for all k in K.
In the talk I will discuss the relationship between the concept of IS and the existence arithmetic structure in the set K, I will focus primarily on the case where K contains arbitrarily long arithmetic progressions with specified lengths and step sizes.
2019 Jan 01

Yotam Smilansky (HUJI), Multiscale substitution schemes and Kakutani sequences of partitions.

2:15pm to 3:15pm

Location: 

Ross 70

Abstract: Substitution schemes provide a classical method for constructing tilings
of Euclidean space. Allowing multiple scales in the scheme, we introduce
a rich family of sequences of tile partitions generated by the substitution
rule, which include the sequence of partitions of the unit interval
considered by Kakutani as a special case. In this talk we will use new path counting
results for directed weighted graphs to show that such sequences
of partitions are uniformly distributed, thus extending Kakutani's
2018 Dec 27

Basic Notions: Sergiu Hart - "Game Dynamics and Equilibria"

4:00pm to 5:00pm

Location: 

Ross 70
The general theme is game dynamics leading to equilibrium concepts.
The plan is to deal with the following topics (all concepts will be defined, and proofs / proof outlines will be provided):
(1) An integral approach to the construction of calibrated forecasts and their use for Nash equilibrium dynamics.
(2) Blackwell's Approachability Theorem and its use for correlated equilibrium dynamics (regret-matching).
(3) Communication complexity and its use for the speed of convergence of uncoupled dynamics.
2019 Jan 03

Basic Notions: Dorit Aharonov - "Quantum computation"

4:00pm to 5:00pm

Location: 

Ross 70
Quantum computation
==================
You can hardly open the newspaper nowadays without seeing something about Quantum computation. But aside from the hype and the industry interest, this deceivingly simple model offers a surprisingly rich set of mathematical, physical and conceptual questions, which seem to touch upon almost any area of mathematics: from group representations, to Markov chains, Knot invariants, expanders, cryptography, lattices, differential geometry, and many more.
2019 Mar 20

Analysis Seminar: Andrei Osipov (Yale) "On the evaluation of sums of periodic Gaussians"

12:00pm to 1:00pm

Location: 

Ross 70
Title:
On the evaluation of sums of periodic Gaussians
Abstract:
Discrete sums of the form
$\sum_{k=1}^N q_k \cdot \exp\left( -\frac{t – s_k}{2 \cdot \sigma^2} \right)$
where $\sigma>0$ and $q_1, \dots, q_N$ are real numbers and
$s_1, \dots, s_N$ and $t$ are vectors in $R^d$,
are frequently encountered in numerical computations across a variety of fields.

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