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X-WR-CALDESC:Events for Discrete Mathematics Group
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DTSTART;TZID=Asia/Seoul:20210401T100000
DTEND;TZID=Asia/Seoul:20210401T110000
DTSTAMP:20260420T143430
CREATED:20210218T001134Z
LAST-MODIFIED:20240705T191014Z
UID:3642-1617271200-1617274800@dimag.ibs.re.kr
SUMMARY:Sophie Spirkl\, Pure pairs in ordered graphs
DESCRIPTION:A pure pair in a graph G is a pair of subsets A\, B of the vertex set of G such that in G\, either all of the edges or none of the edges between A and B are present. Pure pairs have been studied recently motivated by their connections to the Erdos-Hajnal conjecture. \nIn this talk\, I will discuss the topic of pure pairs in ordered graphs\, that is\, graphs with a linear ordering on their vertex set. If we exclude a graph H as an ordered induced subgraph\, how large a pure pair can we guarantee? I will talk about how the answer differs from the case of unordered graphs and show some of the techniques used. \nBased on joint work with Maria Chudnovsky\, Jacob Fox\, Alex Scott\, and Paul Seymour.
URL:https://dimag.ibs.re.kr/event/2021-04-01/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210407T170000
DTEND;TZID=Asia/Seoul:20210407T180000
DTSTAMP:20260420T143430
CREATED:20210301T235812Z
LAST-MODIFIED:20240705T190042Z
UID:3701-1617814800-1617818400@dimag.ibs.re.kr
SUMMARY:Michał Pilipczuk\, Structural properties of powers of sparse graphs
DESCRIPTION:For a graph G and an integer d\, the dth power of G is the graph $G^d$ on the same vertex set as G where two vertices are considered adjacent if and only if they are at distance at most d in G. Assuming that G is sparse\, what can we say about the structure in $G^d$? Certainly $G^d$ can be dense\, as the square of a star is a complete graph\, but $G^d$ still retains many properties that can be derived from the sparsity of G. We will present some recent results in this spirit\, in particular connected to colorings and to the Erdős-Hajnal property\, assuming that G is drawn from a fixed class of bounded expansion or from a fixed nowhere dense class. The talk will be based on the recent papers: “Clustering Powers of Sparse Graphs” (with J. Nešetřil\, P. Ossona de Mendez\, and X. Zhu) and “Erdős-Hajnal properties for powers of sparse graphs” (with M. Briański\, P. Micek\, and M. Seweryn).
URL:https://dimag.ibs.re.kr/event/2021-04-07/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210414T170000
DTEND;TZID=Asia/Seoul:20210414T180000
DTSTAMP:20260420T143430
CREATED:20210301T235620Z
LAST-MODIFIED:20240707T081558Z
UID:3698-1618419600-1618423200@dimag.ibs.re.kr
SUMMARY:István Tomon\, Ramsey properties of semilinear graphs
DESCRIPTION:A graph $G$ is semilinear of bounded complexity if the vertices of $G$ are elements of $\mathbb{R}^{d}$\, and the edges of $G$ are defined by the sign patterns of $t$ linear functions\, where $d$ and $t$ are constants. In this talk\, I will present several results about the symmetric and asymmetric Ramsey properties of semilinear graphs. Some interesting instances of such graphs are intersection graphs of boxes\, interval overlap graphs\, and shift graphs\, so our results extend several well known theorems about the Ramsey and coloring properties of these geometrically defined graphs.
URL:https://dimag.ibs.re.kr/event/2021-04-14/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210421T170000
DTEND;TZID=Asia/Seoul:20210421T180000
DTSTAMP:20260420T143430
CREATED:20210414T142646Z
LAST-MODIFIED:20240705T185049Z
UID:3936-1619024400-1619028000@dimag.ibs.re.kr
SUMMARY:Reinhard Diestel\, Tangles of set separations: a novel clustering method and type recognition in machine learning
DESCRIPTION:Traditional clustering identifies groups of objects that share certain qualities. Tangles do the converse: they identify groups of qualities that typically occur together. They can thereby discover\, relate\, and structure types: of behaviour\, political views\, texts\, or proteins. Tangles offer a new\, quantitative\, paradigm for grouping phenomena rather than things. They can identify key phenomena that allow predictions of others. Tangles also offer a new paradigm for clustering in large data sets.  \nThe mathematical theory of tangles has its origins in the theory of graph minors developed by Robertson and Seymour. It has recently been axiomatized in a way that makes it applicable to a wide range of contexts outside mathematics: from clustering in data science to predicting customer behaviour in economics\, from DNA sequencing and drug development to text analysis and machine learning. \nThis very informal talk will not show you the latest intricacies of abstract tangle theory (for which you can find links on the tangle pages of my website)\, but to win you over to join our drive to develop real tangle applications in areas as indicated above. We have some software to share\, but are looking for people to try it out with us on real-world examples! \nHere are some introductory pages from a book I am writing on this\, which may serve as an extended abstract: https://arxiv.org/abs/2006.01830
URL:https://dimag.ibs.re.kr/event/2021-04-21/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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