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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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TZID:Asia/Seoul
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TZOFFSETFROM:+0900
TZOFFSETTO:+0900
TZNAME:KST
DTSTART:20230101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20240507T163000
DTEND;TZID=Asia/Seoul:20240507T173000
DTSTAMP:20260418T010637
CREATED:20240327T080653Z
LAST-MODIFIED:20240705T153041Z
UID:8434-1715099400-1715103000@dimag.ibs.re.kr
SUMMARY:Tony Huynh\, Aharoni's rainbow cycle conjecture holds up to an additive constant
DESCRIPTION:In 2017\, Aharoni proposed the following generalization of the Caccetta-Häggkvist conjecture for digraphs. If G is a simple n-vertex edge-colored graph with n color classes of size at least r\, then G contains a rainbow cycle of length at most ⌈n/r⌉. \nIn this talk\, we prove that Aharoni’s conjecture holds up to an additive constant. Specifically\, we show that for each fixed r\, there exists a constant c such that if G is a simple n-vertex edge-colored graph with n color classes of size at least r\, then G contains a rainbow cycle of length at most n/r+c. \nThis is joint work with Patrick Hompe.
URL:https://dimag.ibs.re.kr/event/2024-05-07/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20240514T163000
DTEND;TZID=Asia/Seoul:20240514T173000
DTSTAMP:20260418T010637
CREATED:20240329T053414Z
LAST-MODIFIED:20240705T153041Z
UID:8445-1715704200-1715707800@dimag.ibs.re.kr
SUMMARY:Niloufar Fuladi\, Cross-cap drawings and signed reversal distance
DESCRIPTION:A cross-cap drawing of a graph G is a drawing on the sphere with g distinct points\, called cross-caps\, such that the drawing is an embedding except at the cross-caps\, where edges cross properly. A cross-cap drawing of a graph G with g cross-caps can be used to represent an embedding of G on a non-orientable surface of genus g. Mohar conjectured that any triangulation of a non-orientable surface of genus g admits a cross-cap drawing with g cross-caps in which each edge of the triangulation enters each cross-cap at most once. Motivated by Mohar’s conjecture\, Schaefer and Stefankovic provided an algorithm that computes a cross-cap drawing with a minimal number of cross-caps for a graph G such that each edge of the graph enters each cross-cap at most twice. In this talk\, I will first outline a connection between cross-cap drawings and an algorithm coming from computational biology to compute the signed reversal distance between two permutations. This connection will then be leveraged to answer two computational problems on graphs embedded on surfaces. \nFirst\, I show how to compute a “short” canonical decomposition for a non-orientable surface with a graph embedded on it. Such canonical decompositions were known for orientable surfaces\, but the techniques used to compute them do not generalize to non-orientable surfaces due to their more complex nature. Second\, I explain how to build a counter example to a stronger version of Mohar’s conjecture that is stated for pseudo-triangulations. \nThis is joint work with Alfredo Hubard and Arnaud de Mesmay.
URL:https://dimag.ibs.re.kr/event/2024-05-14/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20240521T163000
DTEND;TZID=Asia/Seoul:20240521T173000
DTSTAMP:20260418T010637
CREATED:20231128T002423Z
LAST-MODIFIED:20240705T155114Z
UID:7965-1716309000-1716312600@dimag.ibs.re.kr
SUMMARY:Vadim Lozin\, Graph problems and monotone classes
DESCRIPTION:Very little is known about critical properties of graphs in the hierarchy of monotone classes\, i.e. classes closed under taking (not necessarily induced) subgraphs. We distinguish four important levels in this hierarchy and discuss possible new levels by focusing on the Hamiltonian cycle problem. In particular\, we obtain a number of results for this problem on monotone classes.
URL:https://dimag.ibs.re.kr/event/2024-05-21/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20240528T163000
DTEND;TZID=Asia/Seoul:20240528T173000
DTSTAMP:20260418T010637
CREATED:20240418T043152Z
LAST-MODIFIED:20240705T153011Z
UID:8542-1716913800-1716917400@dimag.ibs.re.kr
SUMMARY:Yongho Shin (신용호)\, Three-way online correlated selection
DESCRIPTION:Two-way online correlated selection (two-way OCS) is an online algorithm that\, at each timestep\, takes a pair of elements from the ground set and irrevocably chooses one of the two elements\, while ensuring negative correlation in the algorithm’s choices. OCS was initially invented by Fahrbach\, Huang\, Tao\, and Zadimoghaddam (FOCS 2020\, JACM 2022) to break a natural long-standing barrier in edge-weighted online bipartite matching. They posed two open questions\, one of which was the following: Can we obtain n-way OCS for $n >2$\, in which the algorithm can be given $n >2$ elements to choose from at each timestep? \nIn this talk\, we affirmatively answer this open question by presenting a three-way OCS which is simple to describe: it internally runs two instances of two-way OCS\, one of which is fed with the output of the other. Contrast to its simple construction\, we face a new challenge in analysis that the final output probability distribution of our three-way OCS is highly elusive since it requires the actual output distribution of two-way OCS. We show how we tackle this challenge by approximating the output distribution of two-way OCS by a flatter distribution serving as a safe surrogate. \nThis is joint work with Hyung-Chan An.
URL:https://dimag.ibs.re.kr/event/2024-05-28/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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