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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
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DTSTART:20250101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260506T163000
DTEND;TZID=Asia/Seoul:20260506T173000
DTSTAMP:20260415T201659
CREATED:20260313T150340Z
LAST-MODIFIED:20260403T110615Z
UID:12435-1778085000-1778088600@dimag.ibs.re.kr
SUMMARY:Maximilian Gorsky\, The Disjoint Paths Problem lies in the Oort cloud of algorithms
DESCRIPTION:In this talk we discuss recent work to that establishes that the bounds of the Vital Linkage Function is single-exponential. This has immediate impacts on the complexity of the k-Disjoint Paths Problem\, Minor Checking\, and more generally\, the Folio-Problem. We in fact prove something even stronger: It turns out that it is not in fact the number of terminals (or more generally vertices) that matters in these problems\, but rather their structure within the graph. Concretely\, we show that the Vital Linkage Function is single-exponential only in the bidimensionality of the terminals\, whilst the number of terminals contributes only polynomially. A direct consequence of this is an algorithm for the k-Disjoint Paths Problem running in $f(k)n^2$-time\, where f(k) is singly exponential in k and doubly exponential in the bidimensionality of k. This derives directly from an algorithm for the Folio-problem we give that has an analogous runtime. Notably these are the first algorithms for these problems in which the function f is explicit. In particular\, we give the first explicit bounds for the Vital Linkage Function. \nJoint work with Dario Cavallaro\, Stephan Kreutzer\, Dimitrios Thilikos\, and Sebastian Wiederrecht.
URL:https://dimag.ibs.re.kr/event/2026-05-06/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260512T163000
DTEND;TZID=Asia/Seoul:20260512T173000
DTSTAMP:20260415T201659
CREATED:20260320T061938Z
LAST-MODIFIED:20260407T022605Z
UID:12453-1778603400-1778607000@dimag.ibs.re.kr
SUMMARY:Benjamin Duhamel\, Excluding a forest induced minor
DESCRIPTION:We give an induced counterpart of the Forest Minor theorem: for any t ≥ 2\, the $K_{t\,t}$-subgraph-free H-induced-minor-free graphs have bounded pathwidth if and only if H belongs to a class F of forests\, which we describe as the induced minors of two (very similar) infinite parameterized families. This constitutes a significant step toward classifying the graphs H for which every weakly sparse H-induced-minor-free class has bounded treewidth. Our work builds on the theory of constellations developed in the Induced Subgraphs and Tree Decompositions series. \nThis is a joint work with É. Bonnet and R. Hickingbotham.
URL:https://dimag.ibs.re.kr/event/2026-05-12/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260519T163000
DTEND;TZID=Asia/Seoul:20260519T173000
DTSTAMP:20260415T201659
CREATED:20251215T012742Z
LAST-MODIFIED:20251215T012742Z
UID:11990-1779208200-1779211800@dimag.ibs.re.kr
SUMMARY:Xavier Goaoc\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2026-05-19/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260526T163000
DTEND;TZID=Asia/Seoul:20260526T173000
DTSTAMP:20260415T201659
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
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