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PRODID:-//Discrete Mathematics Group - ECPv6.15.20//NONSGML v1.0//EN
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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:20220101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20230201T163000
DTEND;TZID=Asia/Seoul:20230201T173000
DTSTAMP:20260418T155108
CREATED:20230115T151551Z
LAST-MODIFIED:20240705T170041Z
UID:6664-1675269000-1675272600@dimag.ibs.re.kr
SUMMARY:Benjamin Bergougnoux\, Tight Lower Bounds for Problems Parameterized by Rank-width
DESCRIPTION:We show that there is no $2^{o(k^2)} n^{O(1)}$ time algorithm for Independent Set on $n$-vertex graphs with rank-width $k$\, unless the Exponential Time Hypothesis (ETH) fails. Our lower bound matches the $2^{O(k^2)} n^{O(1)}$ time algorithm given by Bui-Xuan\, Telle\, and Vatshelle [Discret. Appl. Math.\, 2010] and it answers the open question of Bergougnoux and Kanté [SIAM J. Discret. Math.\, 2021]. We also show that the known $2^{O(k^2)} n^{O(1)}$ time algorithms for Weighted Dominating Set\, Maximum Induced Matching and Feedback Vertex Set parameterized by rank-width $k$ are optimal assuming ETH. Our results are the first tight ETH lower bounds parameterized by rank-width that do not follow directly from lower bounds for $n$-vertex graphs. \nThis is a joint work with Tuukka Korhonen and Jesper Nederlof.\nAccepted to STACS 2023 and available on arXiv https://arxiv.org/abs/2210.02117
URL:https://dimag.ibs.re.kr/event/2023-02-01/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20230215T163000
DTEND;TZID=Asia/Seoul:20230215T173000
DTSTAMP:20260418T155108
CREATED:20230103T235641Z
LAST-MODIFIED:20240705T170041Z
UID:6623-1676478600-1676482200@dimag.ibs.re.kr
SUMMARY:Robert Hickingbotham\, Treewidth\, Circle Graphs and Circular Drawings
DESCRIPTION:A circle graph is an intersection graph of a set of chords of a circle. In this talk\, I will describe the unavoidable induced subgraphs of circle graphs with large treewidth. This includes examples that are far from the `usual suspects’. Our results imply that treewidth and Hadwiger number are linearly tied on the class of circle graphs\, and that the unavoidable induced subgraphs of a vertex-minor-closed class with large treewidth are the usual suspects if and only if the class has bounded rank-width. I will also discuss applications of our results to the treewidth of graphs $G$ that have a circular drawing whose crossing graph is well-behaved in some way. In this setting\, our results show that if the crossing graph is $K_t$-minor-free\, then $G$ has treewidth at most $12t-23$ and has no $K_{2\,4t}$-topological minor. On the other hand\, I’ll present a construction of graphs with arbitrarily large Hadwiger number that have circular drawings whose crossing graphs are $2$-degenerate. This is joint work with Freddie Illingworth\, Bojan Mohar\, and David R. Wood
URL:https://dimag.ibs.re.kr/event/2023-02-15/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20230222T170000
DTEND;TZID=Asia/Seoul:20230222T180000
DTSTAMP:20260418T155108
CREATED:20221115T011207Z
LAST-MODIFIED:20240707T074027Z
UID:6483-1677085200-1677088800@dimag.ibs.re.kr
SUMMARY:Daniel Altman\, On an arithmetic Sidorenko conjecture\, and a question of Alon
DESCRIPTION:Let $G=\mathbb{F}_p^n$. Which systems of linear equations $\Psi$ have the property that amongst all subsets of $G$ of fixed density\, random subsets minimise the number of solutions to $\Psi$? This is an arithmetic analogue of a well-known conjecture of Sidorenko in graph theory\, which has remained open and of great interest since the 1980s. We will discuss some recent results along these lines\, with particular focus on some of the ideas behind a negative answer to a related question of Alon.
URL:https://dimag.ibs.re.kr/event/2023-02-22/
LOCATION:Zoom ID: 224 221 2686 (ibsecopro)
CATEGORIES:Virtual Discrete Math Colloquium
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