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PRODID:-//Discrete Mathematics Group - ECPv6.15.20//NONSGML v1.0//EN
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X-WR-CALNAME:Discrete Mathematics Group
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:20201201T163000
DTEND;TZID=Asia/Seoul:20201201T173000
DTSTAMP:20260419T150729
CREATED:20201115T235924Z
LAST-MODIFIED:20240705T193016Z
UID:3273-1606840200-1606843800@dimag.ibs.re.kr
SUMMARY:Debsoumya Chakraborti\, Rainbow matchings in edge-colored simple graphs
DESCRIPTION:There has been much research on finding a large rainbow matching in a properly edge-colored graph\, where a proper edge coloring is a coloring of the edge set such that no same-colored edges are incident. Barát\, Gyárfás\, and Sárközy conjectured that in every proper edge coloring of a multigraph (with parallel edges allowed\, but not loops) with $2q$ colors where each color appears at least $q$ times\, there is always a rainbow matching of size $q$. We prove that $2q + o(q)$ colors are enough if the graph is simple\, confirming the conjecture asymptotically for simple graphs. We also make progress in the lower bound on the required number of colors for simple graphs\, which disproves a conjecture of Aharoni and Berger. We use a randomized algorithm to obtain a large rainbow matching\, and the analysis of the algorithm is based on differential equations method. We will also briefly comment on the limitations of using our probabilistic approach for the problem. This talk will be based on a joint work with Po-Shen Loh.
URL:https://dimag.ibs.re.kr/event/2020-12-01/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20201202T170000
DTEND;TZID=Asia/Seoul:20201202T180000
DTSTAMP:20260419T150729
CREATED:20201126T022405Z
LAST-MODIFIED:20240705T192124Z
UID:3309-1606928400-1606932000@dimag.ibs.re.kr
SUMMARY:Joonkyung Lee (이준경)\, On common graphs
DESCRIPTION:A graph $H$ is common if the number of monochromatic copies of $H$ in a 2-edge-colouring of the complete graph $K_n$ is minimised by the random colouring. Burr and Rosta\, extending a famous conjecture by Erdős\, conjectured that every graph is common. The conjectures by Erdős and by Burr and Rosta were disproved by Thomason and by Sidorenko\, respectively\, in the late 1980s. \nDespite its importance\, the full classification of common graphs is still a wide open problem and has not seen much progress since the early 1990s. In this lecture\, I will present some old and new techniques to prove whether a graph is common or not.
URL:https://dimag.ibs.re.kr/event/2020-12-02/
LOCATION:Zoom ID:8628398170 (123450)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20201208T163000
DTEND;TZID=Asia/Seoul:20201208T173000
DTSTAMP:20260419T150729
CREATED:20201120T042705Z
LAST-MODIFIED:20240705T193010Z
UID:3287-1607445000-1607448600@dimag.ibs.re.kr
SUMMARY:Hong Liu (刘鸿)\, A solution to Erdős and Hajnal's odd cycle problem
DESCRIPTION:I will go over the history on the study of the set of cycle lengths of graphs with large average degree or chromatic number\, and discuss recent work with Richard Montgomery on this topic. In particular\, we will see the divergence of harmonic sum of odd cycle lengths in graphs with large chromatic number and the appearance of cycle lengths in very sparse sequences (such as powers of 2). The methods developed in this work allows also us to embed equally divided clique subdivisions\, which was conjectured by Thomassen.
URL:https://dimag.ibs.re.kr/event/2020-12-08/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20201222T163000
DTEND;TZID=Asia/Seoul:20201222T173000
DTSTAMP:20260419T150729
CREATED:20201208T060000Z
LAST-MODIFIED:20240705T192115Z
UID:3349-1608654600-1608658200@dimag.ibs.re.kr
SUMMARY:Jinha Kim (김진하)\, On a conjecture by Kalai and Meshulam - the Betti number of the independence complex of ternary graphs
DESCRIPTION:Given a graph G=(V\,E)\, the independence complex of G is the abstract simplicial complex I(G) on V whose faces are the independent sets of G. A graph is ternary if it does not contain an induced cycle of length divisible by three. Kalai and Meshulam conjectured that if G is ternary then the sum of the Betti numbers of I(G) is either 0 or 1. In this talk\, I will introduce a result by Zhang and Wu\, which proves the Kalai-Meshulam conjecture.
URL:https://dimag.ibs.re.kr/event/2020-12-22/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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