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X-ORIGINAL-URL:https://dimag.ibs.re.kr
X-WR-CALDESC:Events for Discrete Mathematics Group
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BEGIN:VTIMEZONE
TZID:Asia/Seoul
BEGIN:STANDARD
TZOFFSETFROM:+0900
TZOFFSETTO:+0900
TZNAME:KST
DTSTART:20190101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20200805T163000
DTEND;TZID=Asia/Seoul:20200805T173000
DTSTAMP:20260423T061253
CREATED:20200629T004613Z
LAST-MODIFIED:20240705T200032Z
UID:2570-1596645000-1596648600@dimag.ibs.re.kr
SUMMARY:Robert Ganian\, Solving Integer Linear Programs by Exploiting Variable-Constraint Interactions
DESCRIPTION:Integer Linear Programming (ILP) is among the most successful and general paradigms for solving computationally intractable optimization problems in computer science. ILP is NP-complete\, and until recently we have lacked a systematic study of the complexity of ILP through the lens of variable-constraint interactions. This changed drastically in recent years thanks to a series of results that together lay out a detailed complexity landscape for the problem centered around the structure of graphical representations of instances. The aim of this talk is to summarize these recent developments and put them into context. Special attention will be paid to the structural parameter treedepth\, and at the end of the talk we will also consider how treedepth can be used to design algorithms for problems beyond ILP.
URL:https://dimag.ibs.re.kr/event/2020-08-05/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20200819T163000
DTEND;TZID=Asia/Seoul:20200819T173000
DTSTAMP:20260423T061253
CREATED:20200629T004729Z
LAST-MODIFIED:20240705T200030Z
UID:2573-1597854600-1597858200@dimag.ibs.re.kr
SUMMARY:Gwenaël Joret\, Packing and covering balls in graphs excluding a minor
DESCRIPTION:In 2007\, Chepoi\, Estellon\, and Vaxès conjectured that there exists a universal constant $c>0$ such that the following holds for every positive integers $r$ and $k$\, and every planar graph $G$: Either $G$ contains $k$ vertex-disjoint balls of radius $r$\, or there is a subset of vertices of size at most $c k$ meeting all balls of radius $r$ in $G$. The key aspect of this conjecture is that the constant $c$ does not depend on the radius $r$ of the balls. If we were to allow this dependency\, then the statement is known to hold\, and in fact it is true in the more general setting of graph classes with bounded expansion (as proved by Dvořák). \nIn this talk I will present a proof of this conjecture. The result we prove is a bit more general: (1) The conjecture holds for every proper minor-closed class of graphs (with the constant $c$ depending on the class)\, and (2) we can even focus on any set of balls in the graph we like\, there is nothing special about taking all balls of a given radius. In other words\, we show that for every proper minor-closed class $C$ of graphs\, there exists a constant $c>0$ such that for every graph $G$ in $C$\, every set $S$ of balls in $G$\, and every positive integer $k$\, either there are $k$ vertex-disjoint balls in $S$\, or there is a subset of vertices of $G$ of size at most $c k$ meeting all balls in $S$. \nJoint work with Nicolas Bousquet\, Wouter Cames van Batenburg\, Louis\nEsperet\, William Lochet\, Carole Muller\, and François Pirot.
URL:https://dimag.ibs.re.kr/event/2020-08-19/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20200826T103000
DTEND;TZID=Asia/Seoul:20200826T113000
DTSTAMP:20260423T061253
CREATED:20200629T004929Z
LAST-MODIFIED:20240705T200027Z
UID:2576-1598437800-1598441400@dimag.ibs.re.kr
SUMMARY:Nick Brettell\, On the graph width parameter mim-width
DESCRIPTION:Maximum induced matching width\, also known as mim-width\, is a width parameter for graphs introduced by Vatshelle in 2012.  This parameter can be defined over branch decompositions of a graph G\, where the width of a vertex partition (X\,Y) in G is the size of a maximum induced matching in the bipartite graph induced by edges of G with one endpoint in X and one endpoint in Y.  In this talk\, I will present a quick overview of mim-width and some key results that highlight why this parameter is of interest from both a theoretical and algorithmic point of view.  I will discuss some recent work regarding the boundedness or unboundedness of mim-width for hereditary classes defined by forbidding one or two induced subgraphs\, and for generalisations of convex graphs.  I will also touch on some interesting applications of this work\, in particular for colouring and list-colouring.  This is joint work with Jake Horsfield\, Andrea Munaro\, Giacomo Paesani\, and Daniel Paulusma.
URL:https://dimag.ibs.re.kr/event/2020-08-26/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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