2018
Jan
15

# Combinatorics Seminar: Leonardo Martinez

11:00am to 12:30pm

Edmond J. Safra Campus The Hebrew University of Jerusalem

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2018
Jan
15

11:00am to 12:30pm

2017
Mar
27

11:00am to 1:00pm

Rothberg B220 (CS bldg)

Speaker: Micha Sharir (Tel Aviv University)

Title: Eliminating depth cycles for lines and triangles, with applications to bounding incidences

Abstract:

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The talk presents three related results.

We first consider the problem of eliminating all depth cycles in a set of n lines in 3-space.

For two lines l_1, l_2 in 3-space (in general position), we say that l_1 lies below l_2 if the

unique vertical line that meets both lines meets l_1 at a point below the point where it meets l_2.

Title: Eliminating depth cycles for lines and triangles, with applications to bounding incidences

Abstract:

---------

The talk presents three related results.

We first consider the problem of eliminating all depth cycles in a set of n lines in 3-space.

For two lines l_1, l_2 in 3-space (in general position), we say that l_1 lies below l_2 if the

unique vertical line that meets both lines meets l_1 at a point below the point where it meets l_2.

2016
Dec
19

11:00am to 1:00pm

Rothberg B220 (CS)

Speaker: Lukas Kühne (University of Bonn)

Title: Heavy hyperplanes in multiarrangements and their freeness

Abstract:

One of the central topics among the theory of hyperplane arrangements is their freeness. Terao's conjecture tries to link the freeness with the combinatorics of an arrangement. One of the few categories of arrangements which satisfy this conjecture consists of 3-dimensional arrangements with an unbalanced Ziegler restriction. This means that the arrangement contains a lot of hyperplanes intersecting in one single line

Title: Heavy hyperplanes in multiarrangements and their freeness

Abstract:

One of the central topics among the theory of hyperplane arrangements is their freeness. Terao's conjecture tries to link the freeness with the combinatorics of an arrangement. One of the few categories of arrangements which satisfy this conjecture consists of 3-dimensional arrangements with an unbalanced Ziegler restriction. This means that the arrangement contains a lot of hyperplanes intersecting in one single line

2017
Dec
11

11:00am to 12:30pm

Eilat Hall at IIAS

Title: The Invisible Hand of Laplace Read more about Combinatorics seminar: Leonard Schulman

2017
Mar
06

11:00am to 1:00pm

Rothberg B220 (CS)

Speaker: Zilin Jiang (Technion)

Title: Relations between Tverberg points and central points

Abstract:

Given 3n lines in general position in the plane, it is always possible to partition them into n triples of lines so that all the triangles, formed by the triples, share a common point. This result is known back in 1988 by J.P. Roudneff. Strangely, in higher dimensions, it is only proved by Roman Karasev for n that is a prime power.

Title: Relations between Tverberg points and central points

Abstract:

Given 3n lines in general position in the plane, it is always possible to partition them into n triples of lines so that all the triangles, formed by the triples, share a common point. This result is known back in 1988 by J.P. Roudneff. Strangely, in higher dimensions, it is only proved by Roman Karasev for n that is a prime power.

2016
Feb
29

Repeats every week every Monday until Mon Jun 13 2016 .

10:30am to 12:30pm10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

10:30am to 12:30pm

B220 Rothberg (CS and Engineering building)

NOTE THE SPECIAL TIME: 11:00--12:30

Speaker: Eyal Ackerman, University of Haifa at Oranim

Title: Coloring points with respect to squares

Abstract:

Is there an absolute constant $m$ such that any finite planar point set can be 2-colored such that every axis-parallel square that contains at least $m$ points contains points of both colors? I will discuss this problem and related ones.

Speaker: Eyal Ackerman, University of Haifa at Oranim

Title: Coloring points with respect to squares

Abstract:

Is there an absolute constant $m$ such that any finite planar point set can be 2-colored such that every axis-parallel square that contains at least $m$ points contains points of both colors? I will discuss this problem and related ones.

2017
Nov
20

11:00am to 12:30pm

IIAS Room 130

Speaker 1: Sria Louis

Title: Asymptotically Almost Every 2r-regular Graph has an Internal Partition

Abstract: An internal partition of a graph is a partitioning of the vertex set into two parts such that for every vertex, at least half of its neighbors are on its side. It is easy to notice that such a partition doesn't always exist (e.g. - cliques), though, both the existence and finding of such a partition - are open problems.

Title: Asymptotically Almost Every 2r-regular Graph has an Internal Partition

Abstract: An internal partition of a graph is a partitioning of the vertex set into two parts such that for every vertex, at least half of its neighbors are on its side. It is easy to notice that such a partition doesn't always exist (e.g. - cliques), though, both the existence and finding of such a partition - are open problems.

2016
Dec
05

11:00am to 1:00pm

B220 Rothberg (CS)

Speaker: Klim Efremenko (TAU)

Title: Testing Equality in Communication Graphs

Abstract:

Let G=(V,E) be a connected undirected graph with k vertices. Suppose

that on each vertex of the graph there is a player having an n-bit

string. Each player is allowed to communicate with its neighbors

according to a (static) agreed communication protocol and the players

must decide, deterministically, if their inputs are all equal. What

is the minimum possible total number of bits transmitted in a protocol

Title: Testing Equality in Communication Graphs

Abstract:

Let G=(V,E) be a connected undirected graph with k vertices. Suppose

that on each vertex of the graph there is a player having an n-bit

string. Each player is allowed to communicate with its neighbors

according to a (static) agreed communication protocol and the players

must decide, deterministically, if their inputs are all equal. What

is the minimum possible total number of bits transmitted in a protocol

2018
Mar
26

2017
Jan
23

11:00am to 1:00pm

Rothberg B220 (CS bldg)

Speaker: Elchanan Mossel (MIT)

Title: Lower Bounds on Same-Set Inner Product in Correlated Spaces

Abstract: Suppose we pick X uniformly from {0,1,2}^n and Y is picked by letting each Y(i) = X(i) or

X(i) + 1 mod 3 with probability 0.5 each independently.

Is it true that for every set S with |S| > c 2^n it holds that the probability that both X and Y are in S is at least g(c) > 0, where g does not depend on the dimension n?

Similar questions were asked before in different contexts. For example,

Title: Lower Bounds on Same-Set Inner Product in Correlated Spaces

Abstract: Suppose we pick X uniformly from {0,1,2}^n and Y is picked by letting each Y(i) = X(i) or

X(i) + 1 mod 3 with probability 0.5 each independently.

Is it true that for every set S with |S| > c 2^n it holds that the probability that both X and Y are in S is at least g(c) > 0, where g does not depend on the dimension n?

Similar questions were asked before in different contexts. For example,

2017
Dec
25

11:00am to 12:30pm

Room 130 at the IIAS

Title: Trace reconstruction for the deletion channel

2016
Nov
21

11:00am to 1:00pm

B220 Rothberg (CS)

Speaker: David Ellis, Queen Mary

Title: Some applications of the $p$-biased measure to Erd\H{o}s-Ko-Rado type problems

Abstract:

Title: Some applications of the $p$-biased measure to Erd\H{o}s-Ko-Rado type problems

Abstract:

2017
May
29

11:00am to 1:00pm

Rothberg B220 (CS bldg)

Speaker: Dmitry Faifman (U Toronto)

Title: The integral geometry of indefinite signature.

Title: The integral geometry of indefinite signature.

2017
Mar
02

12:00pm to 1:00pm

Manchester Building, Room 209

Title: Almost Congruence Extension Property for subgroups of free groups.

Abstract.

The talk essentially based on: https://arxiv.org/abs/1606.02345

Let G be a group and H every normal subgroup N of H is an intersection of some normal subgroup of G with H. The CEP appears in group theory in different context.

The following question seems to be very difficult:

Which finitely generated subgroup of a free group has CEP?

Abstract.

The talk essentially based on: https://arxiv.org/abs/1606.02345

Let G be a group and H every normal subgroup N of H is an intersection of some normal subgroup of G with H. The CEP appears in group theory in different context.

The following question seems to be very difficult:

Which finitely generated subgroup of a free group has CEP?

2017
Feb
09

12:00pm to 1:00pm

Manchester Building, Room 209

Title: The spectral method for geometric colouring problems

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