Events & Seminars

2018 Oct 15

Combinatorics: Tammy Ziegler, HU, "Extending weakly polynomial functions from high rank varieties"

11:00am to 1:00pm

Location: 

Rothberg CS building, room B500, Safra campus, Givat Ram
Speaker: Tammy Ziegler, HU Title: Extending weakly polynomial functions from high rank varieties Abstract: Let k be a field, V a k-vector space, X in V a subset. Say that f: X —> k is weakly polynomial of degree a if its restriction to any isotropic subspace is a polynomial degree of a. We show that if X is a high rank variety then any weakly polynomial function of degree a is the restriction to X of a polynomial of degree a on V. Joint work with D. Kazhdan.
2018 Nov 05

Combinatorics: Ohad Klein, BIU, "Biased halfspaces, noise sensitivity, and local Chernoff inequalities"

11:00am to 1:00pm

Location: 

Rothberg CS bldg, room B500, Safra campus, Givat Ram
Speaker: Ohad Klein, BIU Title: Biased halfspaces, noise sensitivity, and local Chernoff inequalities Abstract: Let X be a random variable defined by X=\sum_i a_i x_i where x_i are independent random variables uniformly distributed in \{-1, 1\}, and a_i in R, the reals. Assume Var(X)=1=sum a_{i}^2. We investigate the tail behavior of the variable X, and apply the results to study halfspace functions f:{-1,1}^{n}-->{-1,1} defined by f(x)=1 (\sum_i a_i x_i > t) for some t in R. A puzzle: Let a = max_{i} |a_{i}|. Is it true that Pr[|X| \leq a] \geq a/10?
2018 Dec 10

Erdos lecture I: Counting linear extensions and Young tableaux

Lecturer: 

Igor Pak (UCLA)
11:00am to 1:00pm

Location: 

IIAS, lecture hall 130, Safra campus, Givat Ram
Speaker: Igor Pak, UCLA Title: Counting linear extensions. Abstract: I will survey various known and recent results on counting the number of linear extensions of finite posets. I will emphasize the asymptotic and complexity aspects for special families, where the problem is especially elegant yet remains #P-complete. In the second half of the talk I will turn to posets corresponding to (skew) Young diagrams. This special case is important for many applications in representation theory and algebraic geometry.
2018 Oct 29

Combinatorics: Noam Lifshitz, BIU, "Sharp thresholds for sparse functions with applications to extremal combinatorics."

11:00am to 1:00pm

Location: 

Rothberg CS blgd, room B500, Safra campus, Givat, Ram
Speaker: Noam Lifshitz, BIU Title: Sharp thresholds for sparse functions with applications to extremal combinatorics. Abstract: The sharp threshold phenomenon is a central topic of research in the analysis of Boolean functions. Here, one aims to give sufficient conditions for a monotone Boolean function $f$ to satisfy $\mu_{p}(f)=o(\mu_{q}(f))$, where $q = p + o(p)$, and $\mu_{p}(f)$ is the probability that $f=1$ on an input with independent coordinates, each taking the value $1$ with probability $p$.
2018 Dec 19

Analysis Seminar: Dmitry Ryabogin (Kent) "On a local version of the fifth Busemann-Petty Problem"

12:00pm to 1:00pm

Location: 

Ross Building, Room 70
Title: On a local version of the fifth Busemann-Petty Problem Abstract: In 1956, Busemann and Petty posed a series of questions about symmetric convex bodies, of which only the first one has been solved. Their fifth problem asks the following. Let K be an origin symmetric convex body in the n-dimensional Euclidean space and let H_x be a hyperplane passing through the origin orthogonal to a unit direction x. Consider a hyperplane G parallel to H_x and supporting to K and let C(K,x)=vol(K\cap H_x)dist (0, G).
2018 Dec 04

Dynamics Seminar: Omri Sarig (Weizmann) Local limit theorems for inhomogeneous Markov chains

2:15pm to 3:15pm

Abstract: An inhomogeneous Markov chain X_n is a Markov chain whose state spaces and transition kernels change in time. A “local limit theorem” is an asymptotic formula for probabilities of th form Prob[S_N-z_N\in (a,b)] , S_N=f_1(X_1,X_2)+....+f_N(X_N,X_{N+1}) in the limit N—>infinity. Here z_N is a “suitable” sequence of numbers. I will describe general sufficient conditions for such results. If time allows, I will explain why such results are needed for the study of certain problems related to irrational rotations. This is joint work with Dmitry Dolgopyat.
2018 Oct 23

Dynamics Seminar: Nishant Chandgotia (HUJI). Some universal models for Z^d actions

2:15pm to 3:15pm

Location: 

Ross 70
Krieger’s generator theorem shows that any free invertible ergodic measure preserving action (Y,\mu, S) can be modelled by A^Z (equipped with the shift action) provided the natural entropy constraint is satisfied; we call such systems (here it is A^Z) universal. Along with Tom Meyerovitch, we establish general specification like conditions under which Z^d-dynamical systems are universal. These conditions are general enough to prove that 1) A self-homeomorphism with almost weak specification on a compact metric space (answering a question by Quas and Soo)

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