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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:20250101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260526T163000
DTEND;TZID=Asia/Seoul:20260526T173000
DTSTAMP:20260506T134912
CREATED:20260112T025344Z
LAST-MODIFIED:20260122T105556Z
UID:12084-1779813000-1779816600@dimag.ibs.re.kr
SUMMARY:Sarah Morell\, Unsplittable Transshipments
DESCRIPTION:We consider an arc-capacitated directed graph $D=(V\,A)$\, where each node $v$ is associated with a rational balance value $b(v)$. Nodes with negative balance values are referred to as sources\, while those with positive balance values are called sinks. A feasible $b$-transshipment is a flow $f : A \to \mathbb{R}_{\ge 0}$ that routes the total supply of the sources to the sinks through $D$\, while respecting the given arc capacity constraints and satisfying the balance requirements at each node. An unsplittable $b$-transshipment additionally requires that\, for each source-sink pair\, the flow sent from that source to that sink is routed along at most one directed path. Unsplittable $b$-transshipments (UT) generalize the well-studied single source unsplittable flow (SSUF) problem in which $D$ contains a single source and multiple sinks\, and each demand must be routed along a single path from the common source to its destination.  \nGiven a feasible $b$-transshipment $f$ that is not necessarily unsplittable\, a natural question is whether there exists an feasible unsplittable $b$-transshipment flow $g$ that approximates $f$ in an arc-wise sense. In particular\, we seek bounds on the maximum deviation $|f_a-g_a|$ over all arcs $a \in A$. For the special case of SSUFs\, Dinitz\, Garg\, and Goemans (Combinatorica 1999) proved that there exists an unsplittable flow $g$ such that $g_a \leq f_a + d_{\max}$ for all $a \in A$\, where $d_{\max}$ denotes the maximum demand value. Jointly with Martin Skutella (Mathematical Programming 2022)\, we studied unsplittable flows with arc-wise lower bounds and showed that there exists an unsplittable flow $g$ satisfying $g_a \ge f_a – d_{\max}$ for all $a \in A$. \n In this talk\, we extend this line of research by adapting the techniques of Dinitz\, Garg\, and Goemans to the more general setting of UTs. We show that\, given any feasible $b$-transshipment $f$\, there exists a feasible unsplittable $b$-transshipment $g$ such that $g_a \leq f_a + d_{\max}$ (resp. $g_a \ge f_a – d_{\max}$) for all $a \in A$.  \n This is joint work with Srinwanti Debgupta and Martin Skutella.
URL:https://dimag.ibs.re.kr/event/2026-05-26/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260602T163000
DTEND;TZID=Asia/Seoul:20260602T173000
DTSTAMP:20260506T134912
CREATED:20251210T144125Z
LAST-MODIFIED:20251225T223707Z
UID:11977-1780417800-1780421400@dimag.ibs.re.kr
SUMMARY:Maria Chudnovsky\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2025-06-02/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260609T163000
DTEND;TZID=Asia/Seoul:20260609T173000
DTSTAMP:20260506T134912
CREATED:20260122T084352Z
LAST-MODIFIED:20260122T084352Z
UID:12117-1781022600-1781026200@dimag.ibs.re.kr
SUMMARY:Martin Milanič\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2026-06-09/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260616T163000
DTEND;TZID=Asia/Seoul:20260616T173000
DTSTAMP:20260506T134912
CREATED:20260420T212857Z
LAST-MODIFIED:20260420T212857Z
UID:12560-1781627400-1781631000@dimag.ibs.re.kr
SUMMARY:J. Pascal Gollin\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2026-06-16/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260710T163000
DTEND;TZID=Asia/Seoul:20260710T173000
DTSTAMP:20260506T134912
CREATED:20260324T141000Z
LAST-MODIFIED:20260505T064804Z
UID:12471-1783701000-1783704600@dimag.ibs.re.kr
SUMMARY:Ting-Wei Chao\, The Oddtown Problem Modulo a Composite Number
DESCRIPTION:A family of sets in $[n]$ is called an $\ell$-Oddtown if the sizes of all sets are not divisible by $\ell$\, but the sizes of pairwise intersections are divisible by $\ell$. The problem was completely solved when $\ell$ is a prime via an elegant linear algebraic method\, showing that the family has size at most $n$. However\, not much was known for composite numbers. By splitting the family into families correspond to each prime factor of $\ell$\, one can show that the number is at most $\omega n$\, where $omega$ is the number of prime factors of $\ell$. We used both combinatorial and Fourier analytic arguments to prove that the number of sets in any $\ell$-Oddtown is at most $\omega n-(2\omega+\varepsilon)\log_2 n$ for most $n\,\ell$.
URL:https://dimag.ibs.re.kr/event/2026-07-10/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260818T163000
DTEND;TZID=Asia/Seoul:20260818T173000
DTSTAMP:20260506T134912
CREATED:20260326T020259Z
LAST-MODIFIED:20260326T020259Z
UID:12486-1787070600-1787074200@dimag.ibs.re.kr
SUMMARY:Jinyoung Park (박진영)\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2026-08-18/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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