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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
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TZOFFSETFROM:+0900
TZOFFSETTO:+0900
TZNAME:KST
DTSTART:20180101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20191105T163000
DTEND;TZID=Asia/Seoul:20191105T173000
DTSTAMP:20260420T164813
CREATED:20191027T113022Z
LAST-MODIFIED:20240707T085941Z
UID:1636-1572971400-1572975000@dimag.ibs.re.kr
SUMMARY:Sun Kim (김선)\, Two identities in Ramanujan’s Lost Notebook with Bessel function series
DESCRIPTION:On page 335 in his lost notebook\, Ramanujan recorded without proofs two identities involving finite trigonometric sums and doubly infinite series of Bessel functions. We proved each of these identities under three different interpretations for the double series\, and showed that they are intimately connected with the classical circle and divisor problems in number theory. Furthermore\, we established many analogues and generalizations of them. This is joint work with Bruce C. Berndt and Alexandru Zaharescu.
URL:https://dimag.ibs.re.kr/event/2019-11-05/
LOCATION:Room 1401\, Bldg. E6-1\, KAIST
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20191112T163000
DTEND;TZID=Asia/Seoul:20191112T173000
DTSTAMP:20260420T164813
CREATED:20190920T115103Z
LAST-MODIFIED:20240705T204218Z
UID:1402-1573576200-1573579800@dimag.ibs.re.kr
SUMMARY:Tony Huynh\, Stable sets in graphs with bounded odd cycle packing number
DESCRIPTION:It is a classic result that the maximum weight stable set problem is efficiently solvable for bipartite graphs.  The recent bimodular algorithm of Artmann\, Weismantel and Zenklusen shows that it is also efficiently solvable for graphs without two disjoint odd cycles.  The complexity of the stable set problem for graphs without $k$ disjoint odd cycles is a long-standing open problem for all other values of $k$.  We prove that under the additional assumption that the input graph is embedded in a surface of bounded genus\, there is a polynomial-time algorithm for each fixed $k$.  Moreover\, we obtain polynomial-size extended formulations for the respective stable set polytopes. \nTo this end\, we show that 2-sided odd cycles satisfy the Erdős-Pósa property in graphs embedded in a fixed surface. This result may be of independent interest and extends a theorem of Kawarabayashi and Nakamoto asserting that odd cycles satisfy the Erdős-Pósa property in graphs embedded in a fixed orientable surface. \nEventually\, our findings allow us to reduce the original problem to the problem of finding a minimum-cost non-negative integer circulation of a certain homology class\, which we prove to be efficiently solvable in our case. \nThis is joint work with Michele Conforti\, Samuel Fiorini\, Gwenaël Joret\, and Stefan Weltge.
URL:https://dimag.ibs.re.kr/event/2019-11-12/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20191119T163000
DTEND;TZID=Asia/Seoul:20191119T173000
DTSTAMP:20260420T164813
CREATED:20190924T042207Z
LAST-MODIFIED:20240707T084346Z
UID:1430-1574181000-1574184600@dimag.ibs.re.kr
SUMMARY:Ruth Luo\, Induced Turán problems for hypergraphs
DESCRIPTION:Let $F$ be a graph. We say that a hypergraph $\mathcal H$ is an induced Berge $F$ if there exists a bijective mapping $f$ from the edges of $F$ to the hyperedges of $\mathcal H$ such that for all $xy \in E(F)$\, $f(xy) \cap V(F) = \{x\,y\}$. In this talk\, we show asymptotics for the maximum number of edges in $r$-uniform hypergraphs with no induced Berge $F$. In particular\, this function is strongly related to the generalized Turán function $ex(n\,K_r\, F)$\, i.e.\, the maximum number of cliques of size $r$ in $n$-vertex\, $F$-free graphs.  Joint work with Zoltan Füredi.
URL:https://dimag.ibs.re.kr/event/2019-11-19/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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DTSTART;TZID=Asia/Seoul:20191121T163000
DTEND;TZID=Asia/Seoul:20191121T173000
DTSTAMP:20260420T164813
CREATED:20191028T154322Z
LAST-MODIFIED:20240707T084339Z
UID:1641-1574353800-1574357400@dimag.ibs.re.kr
SUMMARY:Frédéric Meunier\, Topological bounds for graph representations over any field
DESCRIPTION:Haviv (European Journal of Combinatorics\, 2019) has recently proved that some topological lower bounds on the chromatic number of graphs are also lower bounds on their orthogonality dimension over $\mathbb {R}$. We show that this holds actually for all known topological lower bounds and all fields. We also improve the topological bound he obtained for the minrank parameter over $\mathbb {R}$ – an important graph invariant from coding theory – and show that this bound is actually valid for all fields as well. The notion of independent representation over a matroid is introduced and used in a general theorem having these results as corollaries. Related complexity results are also discussed.\nThis is joint work with Meysam Alishahi.
URL:https://dimag.ibs.re.kr/event/2019-11-21/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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