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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:20210101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220113T163000
DTEND;TZID=Asia/Seoul:20220113T173000
DTSTAMP:20260419T182549
CREATED:20220113T073000Z
LAST-MODIFIED:20240707T080528Z
UID:5009-1642091400-1642095000@dimag.ibs.re.kr
SUMMARY:Ron Aharoni\, A strong version of the Caccetta-Haggkvist conjecture
DESCRIPTION:The Caccetta-Haggkvist conjecture\, one of the best known in graph theory\, is that in a digraph with $n$ vertices in which all outdegrees are at least $n/k$ there is a directed cycle of length at most $k$. This is known for  large values of $k$\, relatively to n\, and asymptotically for n large. A few years ago I offered a generalization: given sets $F_1$\, $\ldots$\, $F_n$ of sets of undirected edges\, each of size at least $n/k$\, there exists a rainbow undirected cycle of length  at most $k$. The directed version is obtained by taking as $F_i$ the set of edges going out of the vertex $v_i$ ($i \le n$)\, with the directions removed. I will tell about recent results on this conjecture\, obtained together with He Guo\, with Beger\, Chudnovsky and Zerbib\, and with DeVos and Holzman.
URL:https://dimag.ibs.re.kr/event/2022-01-13/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220120T163000
DTEND;TZID=Asia/Seoul:20220120T173000
DTSTAMP:20260419T182549
CREATED:20220120T073000Z
LAST-MODIFIED:20240705T175100Z
UID:4564-1642696200-1642699800@dimag.ibs.re.kr
SUMMARY:Ken-ichi Kawarabayashi (河原林 健一)\, Toward Directed Graph Minor Theory
DESCRIPTION:Graph Minor project by Robertson and Seymour is perhaps the deepest theory in Graph Theory. It gives a deep structural characterization of graphs without any graph $H$ as a minor. It also gives many exciting algorithmic consequences. \nIn this work\, I would like to talk about our attempt to extend Graph minor project to directed graphs. Topics include \n1. The directed grid theorem\n2. The directed flat wall theorem\n3. Tangle tree decomposition\n4. Variant of the directed disjoint paths problems\n5. Toward the structure (and decomposition) theorem for H-minor-free digraphs. \nJoint work with Stephan Kreutzer\, O-joung Kwon\, Archontia Giannopoulou.
URL:https://dimag.ibs.re.kr/event/2022-01-20/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220127T163000
DTEND;TZID=Asia/Seoul:20220127T173000
DTSTAMP:20260419T182549
CREATED:20211230T013247Z
LAST-MODIFIED:20240705T180010Z
UID:5080-1643301000-1643304600@dimag.ibs.re.kr
SUMMARY:Bo Ning (宁博)\, Substructures and eigenvalues of graphs: Triangles and quadrilaterals
DESCRIPTION:Our talk will mainly focus on the relationship between substructures and eigenvalues of graphs. We will briefly survey recent developments on a conjecture of Bollobás and Nikiforov and a classical result of Nosal on triangles. In particular\, we shall present counting results for previous spectral theorems on triangles and quadrilaterals. If time allows\, we will give a sketch for the proof of one new counting result on triangles.
URL:https://dimag.ibs.re.kr/event/2022-01-27/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
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