BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Discrete Mathematics Group - ECPv6.15.20//NONSGML v1.0//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-ORIGINAL-URL:https://dimag.ibs.re.kr
X-WR-CALDESC:Events for Discrete Mathematics Group
REFRESH-INTERVAL;VALUE=DURATION:PT1H
X-Robots-Tag:noindex
X-PUBLISHED-TTL:PT1H
BEGIN:VTIMEZONE
TZID:Asia/Seoul
BEGIN:STANDARD
TZOFFSETFROM:+0900
TZOFFSETTO:+0900
TZNAME:KST
DTSTART:20210101T000000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220704T163000
DTEND;TZID=Asia/Seoul:20220704T173000
DTSTAMP:20260420T052454
CREATED:20220704T073000Z
LAST-MODIFIED:20240707T075651Z
UID:5797-1656952200-1656955800@dimag.ibs.re.kr
SUMMARY:Eric Vigoda\, Computational phase transition and MCMC algorithms
DESCRIPTION:This talk will highlight recent results establishing a beautiful computational phase transition for approximate counting/sampling in (binary) undirected graphical models (such as the Ising model or on weighted independent sets). The computational problem is to sample from the equilibrium distribution of the model or equivalently approximate the corresponding normalizing factor known as the partition function. We show that when correlations die off on the infinite D-regular tree then the Gibbs sampler has optimal mixing time of $O(n \log n)$ on any graph of maximum degree D\, whereas when the correlations persist (in the limit) then the sampling/counting problem are NP-hard to approximate.  The Gibbs sampler is a simple Markov Chain Monte Carlo (MCMC) algorithm. Key to these mixing results are a new technique known as spectral independence which considers the pairwise influence of vertices. We show that spectral independence implies an optimal convergence rate for a variety of MCMC algorithms.
URL:https://dimag.ibs.re.kr/event/2022-07-04/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220707T100000
DTEND;TZID=Asia/Seoul:20220707T110000
DTSTAMP:20260420T052454
CREATED:20220707T010000Z
LAST-MODIFIED:20240707T075642Z
UID:5783-1657188000-1657191600@dimag.ibs.re.kr
SUMMARY:Sepehr Hajebi\, Holes\, hubs and bounded treewidth
DESCRIPTION:A hole in a graph $G$ is an induced cycle of length at least four\, and for every hole $H$ in $G$\, a vertex $h\in G\setminus H$ is called a $t$-hub for $H$ if $h$ has at least $t$ neighbor in $H$. Sintiari and Trotignon were the first to construct graphs with arbitrarily large treewidth and no induced subgraph isomorphic to the “basic obstructions\,” that is\, a fixed complete graph\, a fixed complete bipartite graph (with parts of equal size)\, all subdivisions of a fixed wall and line graphs of all subdivisions of a fixed wall. They named their counterexamples “layered wheels” for a good reason: layered wheels contain wheels in abundance\, where a wheel means a hole with a $3$-hub. In accordance\, one may ask whether graphs with no wheel and no induced subgraph isomorphic to the basic obstructions have bounded treewidth. This was also disproved by a recent construction due to Davies. But holes with a $2$-hub cannot be avoided in graphs with large treewidth: graphs containing no hole with a $2$-hub and no induced subgraph isomorphic to the basic obstructions have bounded treewidth. I will present a proof of this result\, and will also give an overview of related works.\nBased on joint work with Tara Abrishami\, Bogdan Alecu\, Maria Chudnovsky\, Sophie Spirkl and Kristina Vušković.
URL:https://dimag.ibs.re.kr/event/2022-07-07/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220711T163000
DTEND;TZID=Asia/Seoul:20220711T173000
DTSTAMP:20260420T052454
CREATED:20220711T073000Z
LAST-MODIFIED:20240707T075632Z
UID:5896-1657557000-1657560600@dimag.ibs.re.kr
SUMMARY:Kevin Hendrey\, Product Structure of Graph Classes with Bounded Treewidth
DESCRIPTION:The strong product $G\boxtimes H$ of graphs $G$ and $H$ is the graph on the cartesian product $V(G)\times V(H)$ such that vertices $(v\,w)$ and $(x\,y)$ are adjacent if and only if $\max\{d_G(v\,x)\,d_H(w\,y)\}=1$. Graph product structure theory aims to describe complicated graphs in terms of subgraphs of strong products of simpler graphs. This area of research was initiated by Dujmović\, Joret\, Micek\, Morin\, Ueckerdt and Wood\, who showed that every planar graph is a subgraph of the strong product of a $H\boxtimes P\boxtimes K_3$ for some path $P$ and some graph $H$ of treewidth at most $3$. In this talk\, I will discuss the product structure of various graph classes of bounded treewidth. As an example\, we show that there is a function $f:\mathbb{N}\rightarrow \mathbb{N}$ such that every planar graph of treewidth at most $k$ is a subgraph of $H\boxtimes K_{f(k)}$ for some graph $H$ of treewidth at most $3$. \nThis is based on joint work with Campbell\, Clinch\, Distel\, Gollin\, Hickingbotham\, Huynh\, Illingworth\, Tamitegama\, Tan and Wood.
URL:https://dimag.ibs.re.kr/event/2022-07-11/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220718T163000
DTEND;TZID=Asia/Seoul:20220718T173000
DTSTAMP:20260420T052454
CREATED:20220622T073000Z
LAST-MODIFIED:20240705T171147Z
UID:5878-1658161800-1658165400@dimag.ibs.re.kr
SUMMARY:Jinyoung Park (박진영)\, Thresholds 1/2
DESCRIPTION:Thresholds for increasing properties of random structures are a central concern in probabilistic combinatorics and related areas. In 2006\, Kahn and Kalai conjectured that for any nontrivial increasing property on a finite set\, its threshold is never far from its “expectation-threshold\,” which is a natural (and often easy to calculate) lower bound on the threshold. \nIn the first talk on Monday\, I will introduce the Kahn-Kalai Conjecture with some motivating examples and then briefly talk about the recent resolution of the Kahn-Kalai Conjecture due to Huy Pham and myself. \nIn the second talk on Tuesday\, I will discuss our proof of the conjecture in detail.
URL:https://dimag.ibs.re.kr/event/2022-07-18/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220719T140000
DTEND;TZID=Asia/Seoul:20220719T160000
DTSTAMP:20260420T052454
CREATED:20220719T050000Z
LAST-MODIFIED:20240705T171145Z
UID:5880-1658239200-1658246400@dimag.ibs.re.kr
SUMMARY:Jinyoung Park (박진영)\, Thresholds 2/2
DESCRIPTION:Thresholds for increasing properties of random structures are a central concern in probabilistic combinatorics and related areas. In 2006\, Kahn and Kalai conjectured that for any nontrivial increasing property on a finite set\, its threshold is never far from its “expectation-threshold\,” which is a natural (and often easy to calculate) lower bound on the threshold. \nIn the first talk on Monday\, I will introduce the Kahn-Kalai Conjecture with some motivating examples and then briefly talk about the recent resolution of the Kahn-Kalai Conjecture due to Huy Pham and myself. \nIn the second talk on Tuesday\, I will discuss our proof of the conjecture in detail.
URL:https://dimag.ibs.re.kr/event/2022-07-19/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20220727T163000
DTEND;TZID=Asia/Seoul:20220727T173000
DTSTAMP:20260420T052454
CREATED:20220727T073000Z
LAST-MODIFIED:20240705T171144Z
UID:5830-1658939400-1658943000@dimag.ibs.re.kr
SUMMARY:Noam Lifshitz\, Product free sets in the alternating group
DESCRIPTION:A subset of a group is said to be product free if it does not contain the product of two elements in it. We consider how large can a product free subset of $A_n$ be? \nIn the talk we will completely solve the problem by determining the largest product free subset of $A_n$. \nOur proof combines a representation theoretic argument due to Gowers\, with an analytic tool called hypercontractivity for global functions. We also make use of a dichotomy between structure and a pseudorandomness notion of functions over the symmetric group known as globalness. \nBased on a joint work with Peter Keevash and Dor Minzer.
URL:https://dimag.ibs.re.kr/event/2022-07-27/
LOCATION:Zoom ID: 870 0312 9412 (ibsecopro) [CLOSED]
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
END:VCALENDAR