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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:20200101T000000
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END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210706T163000
DTEND;TZID=Asia/Seoul:20210706T173000
DTSTAMP:20260418T001727
CREATED:20210518T100610Z
LAST-MODIFIED:20240707T081252Z
UID:4101-1625589000-1625592600@dimag.ibs.re.kr
SUMMARY:Suil O (오수일)\, Eigenvalues and [a\, b]-factors in regular graphs
DESCRIPTION:For positive integers\, $r \ge 3\, h \ge 1\,$ and $k \ge 1$\, Bollobás\, Saito\, and Wormald proved some sufficient conditions for an $h$-edge-connected $r$-regular graph to have a k-factor in 1985. Lu gave an upper bound for the third-largest eigenvalue in a connected $r$-regular graph to have a $k$-factor in 2010. Gu found an upper bound for certain eigenvalues in an $h$-edge-connected $r$-regular graph to have a $k$-factor in 2014. For positive integers $a \le b$\, an even (or odd) $[a\, b]$-factor of a graph $G$ is a spanning subgraph $H$ such that for each vertex $v \in V (G)$\, $d_H(v)$ is even (or odd) and $a \le d_H(v) \le b$. In this talk\, we provide best upper bounds (in terms of $a\, b$\, and $r$) for certain eigenvalues (in terms of $a\, b\, r$\, and $h$) in an $h$-edge-connected $r$-regular graph $G$ to guarantee the existence of an even $[a\, b]$-factor or an odd $[a\, b]$-factor. This result extends the one of Bollobás\, Saito\, and Wormald\, the one of Lu\, and the one of Gu.
URL:https://dimag.ibs.re.kr/event/2021-07-06/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210630T170000
DTEND;TZID=Asia/Seoul:20210630T180000
DTSTAMP:20260418T001727
CREATED:20210617T062135Z
LAST-MODIFIED:20240707T081259Z
UID:4277-1625072400-1625076000@dimag.ibs.re.kr
SUMMARY:Florian Gut and Attila Joó\, Large vertex-flames in uncountable digraphs
DESCRIPTION:The local connectivity  $ \kappa_D(r\,v) $ from $ r $ to $ v $ is defined to be the maximal number of internally disjoint $r\rightarrow v $ paths in $ D $. A spanning subdigraph $ L $ of $ D $ with $  \kappa_L(r\,v)=\kappa_D(r\,v) $ for every $ v\in V-r $ must have at least $ \sum_{v\in V-r}\kappa_D(r\,v) $ edges. It was shown by Lovász that\, maybe surprisingly\, this lower bound is sharp for every finite digraph. The optimality of an $ L $ can be captured by the following characterization: For every $ v\in V-r $ there is a system $ \mathcal{P}_v $ of internally disjoint $ r\rightarrow v $ paths in $ L $ covering all the ingoing edges of $ v $ in $ L $ such that one can choose from  each $ P\in \mathcal{P}_v $ either an edge or an internal vertex in such a way that the resulting set meets every $ r\rightarrow v $ path of $ D $. We prove that every digraph of size at most $ \aleph_1 $  admits such a spanning subdigraph $ L $. The question if this remains true for larger digraphs remains open.
URL:https://dimag.ibs.re.kr/event/2021-06-30/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210629T163000
DTEND;TZID=Asia/Seoul:20210629T173000
DTSTAMP:20260418T001727
CREATED:20210614T232723Z
LAST-MODIFIED:20240707T081306Z
UID:4251-1624984200-1624987800@dimag.ibs.re.kr
SUMMARY:Jeong Ok Choi (최정옥)\, Invertibility of circulant matrices of arbitrary size
DESCRIPTION:In this talk\, we present sufficient conditions to guarantee the invertibility of rational circulant matrices with any given size. These sufficient conditions consist of linear combinations in terms of the entries in the first row with integer coefficients. Using these conditions we show the invertibility of some family of circulant matrices with particular forms of integers generated by a primitive element in $\mathbb{Z}_p$. Also\, the invertibility of circulant 0\, 1-matrices can be argued combinatorially by applying sufficient conditions. This is joint work with Youngmi Hur.
URL:https://dimag.ibs.re.kr/event/2021-06-29/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210622T163000
DTEND;TZID=Asia/Seoul:20210622T173000
DTSTAMP:20260418T001727
CREATED:20210430T062352Z
LAST-MODIFIED:20240705T184213Z
UID:4028-1624379400-1624383000@dimag.ibs.re.kr
SUMMARY:Hongseok Yang (양홍석)\, DAG-symmetries and Symmetry-Preserving Neural Networks
DESCRIPTION:The preservation of symmetry is one of the key tools for designing data-efficient neural networks. A representative example is convolutional neural networks (CNNs); they preserve translation symmetries\, and this symmetry preservation is often attributed to their success in real-world applications. In the machine-learning community\, there is a growing body of work that explores a new type of symmetries\, both discrete and continuous\, and studies neural networks that preserve those symmetries. \nIn this talk\, I will explain what I call DAG-symmetries and our preliminary results on the shape of neural networks that preserve these symmetries. DAG-symmetries are finite variants of DAG-exchangeability developed by Jung\, Lee\, Staton\, and Yang (2020) in the context of probabilistic symmetries. Using these symmetries\, we can express that when a neural network works on\, for instance\, sets of bipartite graphs whose edges are labelled with reals\, the network depends on neither the order of elements in the set nor the identities of vertices of the graphs. I will explain how a group of specific DAG-symmetries is constructed by applying a form of wreath product over a given finite DAG. Then\, I will explain what linear layers of neural networks preserving these symmetries should look like. \nThis is joint work with Dongwoo Oh.
URL:https://dimag.ibs.re.kr/event/2021-06-22/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210616T170000
DTEND;TZID=Asia/Seoul:20210616T180000
DTSTAMP:20260418T001727
CREATED:20210428T010009Z
LAST-MODIFIED:20240705T184215Z
UID:4020-1623862800-1623866400@dimag.ibs.re.kr
SUMMARY:Alan Lew\, Representability and boxicity of simplicial complexes
DESCRIPTION:An interval graph is the intersection graph of a family of intervals in the real line. Motivated by problems in ecology\, Roberts defined the boxicity of a graph G to be the minimal k such that G can be written as the intersection of k interval graphs. \nA natural higher-dimensional generalization of interval graphs is the class d-representable complexes. These are simplicial complexes that carry the information on the intersection patterns of a family of convex sets in $mathbb R^d$. We define the d-boxicity of a simplicial complex X to be the minimal k such that X can be written as the intersection of k d-representable complexes. \nA classical result of Roberts\, later rediscovered by Witsenhausen\, asserts that the boxicity of a graph with n vertices is at most n/2. Our main result is the following high dimensional extension of Roberts’ theorem: Let X be a simplicial complex on n vertices with minimal non-faces of dimension at most d. Then\, the d-boxicity of X is at most $frac{1}{d+1}binom{n}{d}$. \nExamples based on Steiner systems show that our result is sharp. The proofs combine geometric and topological ideas.
URL:https://dimag.ibs.re.kr/event/2021-06-16/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210608T150000
DTEND;TZID=Asia/Seoul:20210608T160000
DTSTAMP:20260418T001727
CREATED:20210514T092018Z
LAST-MODIFIED:20240707T081316Z
UID:4080-1623164400-1623168000@dimag.ibs.re.kr
SUMMARY:O-joung Kwon (권오정)\, Classes of intersection digraphs with good algorithmic properties
DESCRIPTION:An intersection digraph is a digraph where every vertex $v$ is represented by an ordered pair $(S_v\, T_v)$ of sets such that there is an edge from $v$ to $w$ if and only if $S_v$ and $T_w$ intersect. An intersection digraph is reflexive if $S_v\cap T_v\neq \emptyset$ for every vertex $v$. Compared to well-known undirected intersection graphs like interval graphs and permutation graphs\, not many algorithmic applications on intersection digraphs have been developed. \nMotivated by the successful story on algorithmic applications of intersection graphs using a graph width parameter called mim-width\, we introduce its directed analogue called `bi-mim-width’ and prove that various classes of reflexive intersection digraphs have bounded bi-mim-width. In particular\, we show that as a natural extension of $H$-graphs\, reflexive $H$-digraphs have linear bi-mim-width at most $12|E(H)|$\, which extends a bound on the linear mim-width of $H$-graphs [On the Tractability of Optimization Problems on $H$-Graphs. Algorithmica 2020] \nFor applications\, we introduce a novel framework of directed versions of locally checkable problems\, that streamlines the definitions and the study of many problems in the literature and facilitates their common algorithmic treatment. We obtain unified polynomial-time algorithms for these problems on digraphs of bounded bi-mim-width\, when a branch decomposition is given. Locally checkable problems include Kernel\, Dominating Set\, and Directed $H$-Homomorphism. \nThis seminar is a part of the\n“Round the World Relay in Combinatorics”\non June 8\, 2021.\nhttp://people.maths.ox.ac.uk/scott/relay.htm \n\n2:00 UTC\, 11:00 KST Melbourne (Australia) Monash University\nDavid Wood (Monash University)\, Universality in Minor-Closed Graph Classes\n3:00 UTC\, 12:00 KST Shanghai (China) Shanghai Center for Mathematical Sciences\nBaogang Xu (Nanjing Normal University\, China)\, On coloring of graphs of girth 2l+1 without longer odd holes\n4:00 UTC\, 13:00 KST Auckland (New Zealand) The University of Auckland\nJeroen Schillewaert (University of Auckland)\, Constructing highly regular expanders from hyperbolic Coxeter groups\n5:00 UTC\, 14:00 KST Sydney (Australia) Combinatorial Mathematics Society of Australasia\nGordon Royle (University of Western Australia (UWA))\, Real chromatic roots of planar graphs\n6:00 UTC\, 15:00 KST Daejeon (Korea) IBS Discrete Mathematics Group\nO-joung Kwon (Incheon National University and IBS Discrete Mathematics Group)\, Classes of intersection digraphs with good algorithmic properties\n7:00 UTC\, 16:00 KST Krakow (Poland) Jagiellonian University\nBartosz Walczak (Jagiellonian)\, Coloring polygon visibility graphs and their generalizations\n8:00 UTC\, 17:00 KST Glasgow (UK) University of Glasgow\nHeng Guo (University of Edinburgh)\, A Markov chain approach towards the sampling Lovász local lemma\n9:00 UTC\, 18:00 KST London (UK) London School of Economics\nAnnika Heckel (LMU)\, How does the chromatic number of a random graph vary?\n10:00 UTC\, 19:00 KST Moscow (Russia) Moscow Institute of Physics and Technology\nNoga Alon (Princeton and Tel Aviv)\n11:00 UTC\, 20:00 KST Budapest (Hungary) Hungarian Academy of Sciences + Eötvös Loránd University\nLászló Lovász (Eotvos University\, Budapest)\n12:00 UTC\, 21:00 KST Bordeaux (France) LaBRI\nCarla Groenland (Utrecht University)\, Universal Graphs and Labelling Schemes\n13:00 UTC\, 22:00 KST New York (USA) City University of New York + Montclair State University + Hofstra University\nDeepak Bal (Montclair State University)\n14:00 UTC\, 23:00 KST Prague (Czech) Czech Academy of Sciences + Czech Technical University + London School of Economics\nDhruv Mubayi (University of Illinois at Chicago)\, The feasible region of hypergraphs\n15:00 UTC\, 00:00 KST Brno (Czech) Masaryk University\nJames Davies (University of Waterloo)\, Colouring circle graphs and their generalisations\n16:00 UTC\, 01:00 KST Oxford (UK) University of Oxford\nJacob Fox (Stanford University)\, Removal lemmas\n17:00 UTC\, 02:00 KST Columbus (USA) Ohio State University\nAllan Sly (Princeton University)\n18:00 UTC\, 03:00 KST Rio (Brazil) Instituto de Matemática Pura e Aplicada\nMarcelo Campos (IMPA)\, The singularity probability of a random symmetric matrix is exponentially small\n19:00 UTC\, 04:00 KST Atlanta (USA) Georgia Institute of Technology\nJim Geelen (University of Waterloo)\, Homomorphisms and colouring for graphs and binary matroids\n20:00 UTC\, 05:00 KST Santiago (Chile) Universidad de Chile\nDavid Conlon (Caltech)\n21:00 UTC\, 06:00 KST Burnaby (Canada) Simon Fraser University\nFan Chung (UCSD)\, Trees and forests in Green’s functions of a graph\n22:00 UTC\, 07:00 KST Victoria (Canada) University of Victoria\nAndrew Suk (UCSD)\, Turán-type problems for point-line incidences\n23:00 UTC\, 08:00 KST Fairbanks (USA) University of Alaska\nRon Gould (Emory)\, Chorded cycles\n\n 
URL:https://dimag.ibs.re.kr/event/2021-06-08/
LOCATION:Zoom ID: 875 9395 3555 (relay) [CLOSED]
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210602T170000
DTEND;TZID=Asia/Seoul:20210602T180000
DTSTAMP:20260418T001727
CREATED:20210506T022454Z
LAST-MODIFIED:20240705T184206Z
UID:4042-1622653200-1622656800@dimag.ibs.re.kr
SUMMARY:Adam Zsolt Wagner\, Constructions in combinatorics via neural networks
DESCRIPTION:Recently\, significant progress has been made in the area of machine learning algorithms\, and they have quickly become some of the most exciting tools in a scientist’s toolbox. In particular\, recent advances in the field of reinforcement learning have led computers to reach superhuman level play in Atari games and Go\, purely through self-play. In this talk\, I will give a very basic introduction to neural networks and reinforcement learning algorithms. I will also indicate how these methods can be adapted to the “game” of trying to find a counterexample to a mathematical conjecture\, and show some examples where this approach was successful.
URL:https://dimag.ibs.re.kr/event/2021-06-02/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210601T163000
DTEND;TZID=Asia/Seoul:20210601T173000
DTSTAMP:20260418T001727
CREATED:20210517T132410Z
LAST-MODIFIED:20240707T081332Z
UID:4091-1622565000-1622568600@dimag.ibs.re.kr
SUMMARY:Doowon Koh (고두원)\, Mattila-Sjölin type functions: A finite field model
DESCRIPTION:Let $\mathbb{F}_q$ be a finite field of order $q$ which is a prime power. In the finite field setting\, we say that a function $\phi\colon \mathbb{F}_q^d\times \mathbb{F}_q^d\to \mathbb{F}_q$ is a Mattila-Sjölin type function in $\mathbb{F}_q^d$ if for any $E\subset \mathbb{F}_q^d$ with $|E|\gg q^{\frac{d}{2}}$\, we have $\phi(E\, E)=\mathbb{F}_q$. The main purpose of this talk is to present the existence of such a function. More precisely\, we will construct a concrete function $\phi: \mathbb{F}_q^4\times \mathbb{F}_q^4\to \mathbb{F}_q$ with $q\equiv 3 \mod{4}$ such that if $E\subset \mathbb F_q^4$ with $|E|>q^2\,$ then $\phi(E\,E)=\mathbb F_q$. This is a joint work with Daewoong Cheong\, Thang Pham\, and Chun-Yen Shen.
URL:https://dimag.ibs.re.kr/event/2021-06-01/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210526T170000
DTEND;TZID=Asia/Seoul:20210526T180000
DTSTAMP:20260418T001727
CREATED:20210424T122241Z
LAST-MODIFIED:20240707T081338Z
UID:3986-1622048400-1622052000@dimag.ibs.re.kr
SUMMARY:Dimitrios M. Thilikos\, Bounding Obstructions sets: the cases of apices of minor closed classes
DESCRIPTION:Given a minor-closed graph class ${\cal G}$\, the (minor) obstruction of ${\cal G}$ is the set of all minor-minimal graphs not in ${\cal G}$. Given a non-negative integer $k$\, we define the $k$-apex of ${\cal A}$ as the class containing every graph $G$ with a set $S$ of vertices whose removal from $G$ gives a graph on ${\cal G}$. We prove that every obstruction of the $k$-apex of ${\cal G}$ has size bounded by some 4-fold exponential function of $p(k)$ where p is a polynomial function whose degree depends on the size of the minor-obstructions of ${\cal G}$. This bound drops to a 2-fold exponential one when ${\cal G}$ excludes some apex graph as a minor (i.e.\, a graph in the $1$-apex of planar graphs). \nJoint work with Ignasi Sau and Giannos Stamoulis.
URL:https://dimag.ibs.re.kr/event/2021-05-26/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210525T163000
DTEND;TZID=Asia/Seoul:20210525T173000
DTSTAMP:20260418T001727
CREATED:20210520T102659Z
LAST-MODIFIED:20240707T081345Z
UID:4112-1621960200-1621963800@dimag.ibs.re.kr
SUMMARY:Ben Lund\, Limit shape of lattice Zonotopes
DESCRIPTION:A convex lattice polytope is the convex hull of a set of integral points. Vershik conjectured the existence of a limit shape for random convex lattice polygons\, and three proofs of this conjecture were given in the 1990s by Bárány\, by Vershik\, and by Sinai. To state this old result more precisely\, there is a convex curve $L \subset [0\,1]^2$ such that the following holds. Let $P$ be a convex lattice polygon chosen uniformly at random from the set of convex lattice polygons with vertices in $[0\,N]^2$. Then\, for $N$ sufficiently large\, $(1/N)P$ will be arbitrarily close (in Hausdorff distance) to $L$ with high probability. It is an open question whether there exists a limit shape for three dimensional polyhedra. \nI will discuss this problem and some relatives\, as well as joint work with Bárány and Bureaux on the existence of a limit shape for lattice zonotopes in all dimensions.
URL:https://dimag.ibs.re.kr/event/2021-05-25/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210521T170000
DTEND;TZID=Asia/Seoul:20210521T180000
DTSTAMP:20260418T001727
CREATED:20210319T050153Z
LAST-MODIFIED:20240705T190024Z
UID:3818-1621616400-1621620000@dimag.ibs.re.kr
SUMMARY:Benjamin Bumpus\, Directed branch-width: A directed analogue of tree-width
DESCRIPTION:Many problems that are NP-hard in general become tractable on `structurally recursive’ graph classes. For example\, consider classes of bounded tree- or clique-width. Since the 1990s\, many directed analogues of tree-width have been proposed. However\, many natural problems (e.g. directed HamiltonPath and MaxCut) remain intractable on such digraph classes of `bounded width’. \nIn this talk\, I will introduce a new tree-width analogue for digraphs called directed branch-width which allows us to define digraph classes for which many problems (including directed HamiltonPath and MaxCut)  become linear-time solvable. Furthermore\, via the definition of directed branch-width\, I will obtain a generalisation to digraphs of Gurski and Wanke’s characterization of graph classes of bounded tree-width in terms of their line graphs. \nThis is joint work with Kitty Meeks and William Pettersson.
URL:https://dimag.ibs.re.kr/event/2021-05-21/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210518T163000
DTEND;TZID=Asia/Seoul:20210518T173000
DTSTAMP:20260418T001727
CREATED:20210420T015329Z
LAST-MODIFIED:20240705T185044Z
UID:3967-1621355400-1621359000@dimag.ibs.re.kr
SUMMARY:Pascal Gollin\, Enlarging vertex-flames in countable digraphs
DESCRIPTION:A rooted digraph is a vertex-flame if for every vertex v there is a set of internally disjoint directed paths from the root to v whose set of terminal edges covers all ingoing edges of v. It was shown by Lovász that every finite rooted digraph admits a spanning subdigraph which is a vertex-flame and large\, where the latter means that it preserves the local connectivity to each vertex from the root. A structural generalisation of vertex-flames and largeness to infinite digraphs was given by Joó and the analogue of Lovász’ result for countable digraphs was shown. \nIn this talk\, I present a strengthening of this result stating that in every countable rooted digraph each vertex-flame can be extended to a large vertex-flame. \nJoint work with Joshua Erde and Attila Joó.
URL:https://dimag.ibs.re.kr/event/2021-05-18/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210512T170000
DTEND;TZID=Asia/Seoul:20210512T180000
DTSTAMP:20260418T001727
CREATED:20210319T045925Z
LAST-MODIFIED:20240705T190026Z
UID:3816-1620838800-1620842400@dimag.ibs.re.kr
SUMMARY:Johannes Carmesin\, A Whitney type theorem for surfaces: characterising graphs with locally planar embeddings
DESCRIPTION:Given a graph\, how do we construct a surface so that the graph embeds in that surface in an optimal way? Thomassen showed that for minimum genus as optimality criterion\, this problem would be NP-hard. Instead of minimum genus\, here we use local planarity — and provide a polynomial algorithm. \nOur embedding method is based on Whitney’s trick to use matroids to construct embeddings in the plane. Consequently we obtain a characterisation of the graphs admitting locally planar embeddings in surfaces in terms of a certain matroid being co-graphic.
URL:https://dimag.ibs.re.kr/event/2021-05-12/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210511T163000
DTEND;TZID=Asia/Seoul:20210511T173000
DTSTAMP:20260418T001727
CREATED:20210420T015716Z
LAST-MODIFIED:20240705T185043Z
UID:3969-1620750600-1620754200@dimag.ibs.re.kr
SUMMARY:Mark Siggers\, The list switch homomorphism problem for signed graphs
DESCRIPTION:A signed graph is a graph in which each edge has a positive or negative sign. Calling two graphs switch equivalent if one can get from one to the other by the iteration of the local action of switching all signs on edges incident to a given vertex\, we say that there is a switch homomorphism from a signed graph $G$ to a signed graph $H$ if there is a sign preserving homomorphism from $G’$ to $H$ for some graph $G’$ that is switch equivalent to $G$.  By reductions to CSP this problem\, and its list version\, are known to be either polynomial time solvable or NP-complete\, depending on $H$.  Recently those signed graphs $H$ for which the switch homomorphism problem is in $P$ were characterised.  Such a characterisation is yet unknown for the list version of the problem. \nWe talk about recent work towards such a characterisation and about how these problems fit in with bigger questions that still remain around the recent CSP dichotomy theorem.
URL:https://dimag.ibs.re.kr/event/2021-05-11/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210506T161500
DTEND;TZID=Asia/Seoul:20210506T171500
DTSTAMP:20260418T001727
CREATED:20210427T013100Z
LAST-MODIFIED:20240705T185031Z
UID:4010-1620317700-1620321300@dimag.ibs.re.kr
SUMMARY:Hong Liu\, Sublinear expander and embeddings sparse graphs
DESCRIPTION:A notion of sublinear expander has played a central role in the resolutions of a couple of long-standing conjectures in embedding problems in graph theory\, including e.g. the odd cycle problem of Erdős and Hajnal that the harmonic sum of odd cycle length in a graph diverges with its chromatic number. I will survey some of these developments.
URL:https://dimag.ibs.re.kr/event/2021-05-06-2/
LOCATION:Zoom
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210506T100000
DTEND;TZID=Asia/Seoul:20210506T110000
DTSTAMP:20260418T001727
CREATED:20210319T045807Z
LAST-MODIFIED:20240705T190027Z
UID:3813-1620295200-1620298800@dimag.ibs.re.kr
SUMMARY:Raul Lopes\, Adapting the Directed Grid Theorem into an FPT Algorithm
DESCRIPTION:The Grid Theorem of Robertson and Seymour [JCTB\, 1986] is one of the most important tools in the field of structural graph theory\, finding numerous applications in the design of algorithms for undirected graphs. An analogous version of the Grid Theorem in digraphs was conjectured by Johnson et al. [JCTB\, 2001] \, and proved by Kawarabayashi and Kreutzer [STOC\, 2015]. They showed that there is a function f(k) such that every digraph of directed tree-width at least f(k) contains a cylindrical grid of order k as a butterfly minor and stated that their proof can be turned into an XP algorithm\, with parameter k\, that either constructs a decomposition of the appropriate width\, or finds the claimed large cylindrical grid as a butterfly minor. \nIn this talk\, we present the ideas used in our adaptation of the Directed Grid Theorem into an FPT algorithm. We provide two FPT algorithms with parameter k. The first one either produces an arboreal decomposition of width 3k-2 or finds a haven of order k in a digraph D. The second one uses a bramble B that naturally occurs in digraphs of large directed tree-width to find a well-linked set of order k that is contained in the set of vertices of a path hitting all elements of B. As tools to prove these results\, we show how to solve a generalized version of the problem of finding balanced separators for a given set of vertices T in FPT time with parameter |T|. \nJoint work with Victor Campos\, Ana Karolinna Maia\, and Ignasi Sau.
URL:https://dimag.ibs.re.kr/event/2021-05-06/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210430T090000
DTEND;TZID=Asia/Seoul:20210430T122000
DTSTAMP:20260418T001727
CREATED:20210315T005534Z
LAST-MODIFIED:20240707T081537Z
UID:3794-1619773200-1619785200@dimag.ibs.re.kr
SUMMARY:Extremal and Probabilistic Combinatorics (2021 KMS Spring Meeting)
DESCRIPTION:A special session “Extremal and Probabilistic Combinatorics” at the 2021 KMS Spring Meeting is organized by Tuan Tran. \nURL: https://www.kms.or.kr/meetings/spring2021/ \nSpeakers and Schedule\nAll talks are on April 30. \n\n[9:00 am] Joonkyung Lee (이준경)\, University College London\n\nMajority dynamics on sparse random graphs\n\n\n[9:30 am] Dong Yeap Kang (강동엽)\, Unversity of Birmingham\n\nThe Erdős-Faber-Lovász conjecture and related results\n\n\n[10:00 am] Jinyoung Park (박진영)\, IAS\n\nThe threshold for the square of a Hamilton cycle\n\n\n[10:50 am] Debsoumya Chakraborti\, IBS Discrete Mathematics Group\n\nGeneralized graph saturation\n\n\n[11:20 am] Jaehoon Kim (김재훈)\, KAIST\n\nResolution of the Oberwolfach problem\n\n\n[11:50 am] Hong Liu\, University of Warwick\n\nSublinear expanders and its applications\n\n\n\n\n\n\nAbstracts\nDebsoumya Chakraborti\, Generalized graph saturation\nGraph saturation is one of the oldest areas of investigation in extremal combinatorics. A graph G is called F-saturated if G does not contain a subgraph isomorphic to F\, but the addition of any edge creates a copy of F. We resolve one of the most fundamental questions of minimizing the number of cliques of size r in a $K_s$-saturated graph for all sufficiently large numbers of vertices\, confirming a conjecture of Kritschgau\, Methuku\, Tait and Timmons. We further prove a corresponding stability result. This talk will be based on joint work with Po-Shen Loh. \nJaehoon Kim (김재훈)\, Resolution of the Oberwolfach problem\nThe Oberwolfach problem\, posed by Ringel in 1967\, asks for a decomposition of $K_{2n+1}$ into edge-disjoint copies of a given 2-factor. We show that this can be achieved for all large n. We actually prove a significantly more general result\, which allows for decompositions into more general types of factors. \nDong Yeap Kang (강동엽)\, The Erdős-Faber-Lovász conjecture and related results\nA hypergraph is linear if every pair of two distinct edges shares at most one vertex. A longstanding conjecture by Erdős\, Faber\, and Lovász in 1972\, states that the chromatic index of any linear hypergraph on n vertices is at most n. \nIn this talk\, I will present the ideas to prove the conjecture for all large n. This is joint work with Tom Kelly\, Daniela Kühn\, Abhishek Methuku\, and Deryk Osthus. \n  \nJoonkyung Lee (이준경)\, Majority dynamics on sparse random graphs\nMajority dynamics on a graph G is a deterministic process such that every vertex updates its {-1\,1}-assignment according to the majority assignment on its neighbor simultaneously at each step. Benjamini\, Chan\, O’Donnell\, Tamuz and Tan conjectured that\, in the Erdős-Rényi random graph G(n\,p)\, the random initial {-1\,1}-assignment converges to the unanimity with high probability whenever p>> 1/n. \nThis conjecture was firstly confirmed for $p>Cn^{-1/2}$ for a large constant C>0 by Fountoulakis\, Kang and Makai. Although this result has been reproved recently by Tran and Vu and by Berkowitz and Devlin\, none of them managed to extend it beyond the barrier $p>Cn^{-1/2}$. We prove the conjecture for sparser random graphs G(n\,p)\, where $Dn^{-3/5}\log n < p < C n^{-1/2}$ with a large constant D>0. \nJoint work with Debsoumya Chakraborti\, Jeong Han Kim and Tuan Tran. \nHong Liu\, Sublinear expanders and its applications\nI will review the history of sublinear expander and present some recent applications\, which lead to resolutions of several long-standing problems in sparse graphs embeddings. \nJinyoung Park (박진영)\, The threshold for the square of a Hamilton cycle\nWe will talk about a recent result of Jeff Kahn\, Bhargav Narayanan\, and myself stating that the threshold for the random graph G(n\,p) to contain the square of a Hamilton cycle is $1/\sqrt n$\, resolving a conjecture of Kühn and Osthus from 2012. The proof idea is motivated by the recent work of Frankston and the three aforementioned authors on a conjecture of Talagrand — “a fractional version of Kahn-Kalai expectation threshold conjecture.”
URL:https://dimag.ibs.re.kr/event/2021-04-30/
CATEGORIES:Workshops and Conferences
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210427T163000
DTEND;TZID=Asia/Seoul:20210427T173000
DTSTAMP:20260418T001727
CREATED:20210419T130854Z
LAST-MODIFIED:20240705T185048Z
UID:3961-1619541000-1619544600@dimag.ibs.re.kr
SUMMARY:Jungho Ahn (안정호)\, Well-partitioned chordal graphs with the obstruction set and applications
DESCRIPTION:We introduce a new subclass of chordal graphs that generalizes split graphs\, which we call well-partitioned chordal graphs. Split graphs are graphs that admit a partition of the vertex set into cliques that can be arranged in a star structure\, the leaves of which are of size one. Well-partitioned chordal graphs are a generalization of this concept in the following two ways. First\, the cliques in the partition can be arranged in a tree structure\, and second\, each clique is of arbitrary size. We mainly provide a characterization of well-partitioned chordal graphs by forbidden induced subgraphs and give a polynomial-time algorithm that given any graph\, either finds an obstruction or outputs a partition of its vertex set that asserts that the graph is well-partitioned chordal. We demonstrate the algorithmic use of this graph class by showing that two variants of the problem of finding pairwise disjoint paths between k given pairs of vertices are in FPT\, parameterized by k\, on well-partitioned chordal graphs\, while on chordal graphs\, these problems are only known to be in XP. From the other end\, we introduce some problems that are polynomial-time solvable on split graphs but become NP-complete on well-partitioned chordal graphs. \nThis is joint work with Lars Jaffke\, O-joung Kwon\, and Paloma T. Lima.
URL:https://dimag.ibs.re.kr/event/2021-04-27/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210421T170000
DTEND;TZID=Asia/Seoul:20210421T180000
DTSTAMP:20260418T001727
CREATED:20210414T142646Z
LAST-MODIFIED:20240705T185049Z
UID:3936-1619024400-1619028000@dimag.ibs.re.kr
SUMMARY:Reinhard Diestel\, Tangles of set separations: a novel clustering method and type recognition in machine learning
DESCRIPTION:Traditional clustering identifies groups of objects that share certain qualities. Tangles do the converse: they identify groups of qualities that typically occur together. They can thereby discover\, relate\, and structure types: of behaviour\, political views\, texts\, or proteins. Tangles offer a new\, quantitative\, paradigm for grouping phenomena rather than things. They can identify key phenomena that allow predictions of others. Tangles also offer a new paradigm for clustering in large data sets.  \nThe mathematical theory of tangles has its origins in the theory of graph minors developed by Robertson and Seymour. It has recently been axiomatized in a way that makes it applicable to a wide range of contexts outside mathematics: from clustering in data science to predicting customer behaviour in economics\, from DNA sequencing and drug development to text analysis and machine learning. \nThis very informal talk will not show you the latest intricacies of abstract tangle theory (for which you can find links on the tangle pages of my website)\, but to win you over to join our drive to develop real tangle applications in areas as indicated above. We have some software to share\, but are looking for people to try it out with us on real-world examples! \nHere are some introductory pages from a book I am writing on this\, which may serve as an extended abstract: https://arxiv.org/abs/2006.01830
URL:https://dimag.ibs.re.kr/event/2021-04-21/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210420T163000
DTEND;TZID=Asia/Seoul:20210420T173000
DTSTAMP:20260418T001727
CREATED:20210416T123209Z
LAST-MODIFIED:20240705T185049Z
UID:3946-1618936200-1618939800@dimag.ibs.re.kr
SUMMARY:Sang-il Oum (엄상일)\, What is an isotropic system?
DESCRIPTION:Bouchet introduced isotropic systems in 1983 unifying some combinatorial features of binary matroids and 4-regular graphs. The concept of isotropic system is a useful tool to study vertex-minors of graphs and yet it is not well  known. I will give an introduction to isotropic systems.
URL:https://dimag.ibs.re.kr/event/2021-04-20/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210414T170000
DTEND;TZID=Asia/Seoul:20210414T180000
DTSTAMP:20260418T001727
CREATED:20210301T235620Z
LAST-MODIFIED:20240707T081558Z
UID:3698-1618419600-1618423200@dimag.ibs.re.kr
SUMMARY:István Tomon\, Ramsey properties of semilinear graphs
DESCRIPTION:A graph $G$ is semilinear of bounded complexity if the vertices of $G$ are elements of $\mathbb{R}^{d}$\, and the edges of $G$ are defined by the sign patterns of $t$ linear functions\, where $d$ and $t$ are constants. In this talk\, I will present several results about the symmetric and asymmetric Ramsey properties of semilinear graphs. Some interesting instances of such graphs are intersection graphs of boxes\, interval overlap graphs\, and shift graphs\, so our results extend several well known theorems about the Ramsey and coloring properties of these geometrically defined graphs.
URL:https://dimag.ibs.re.kr/event/2021-04-14/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210413T163000
DTEND;TZID=Asia/Seoul:20210413T173000
DTSTAMP:20260418T001727
CREATED:20210329T063026Z
LAST-MODIFIED:20240705T190013Z
UID:3866-1618331400-1618335000@dimag.ibs.re.kr
SUMMARY:William Overman\, Some Ordered Ramsey Numbers of Graphs on Four Vertices
DESCRIPTION:Ordered Ramsey numbers were introduced in 2014 by Conlon\, Fox\, Lee\, and Sudakov. Their results included upper bounds for general graphs and lower bounds showing separation from classical Ramsey numbers. We show the first nontrivial results for ordered Ramsey numbers of specific small graphs. In particular we prove upper bounds for orderings of graphs on four vertices\, and determine some numbers exactly using  SAT solvers for lower bounds. These results are in the spirit of exact calculations for classical Ramsey numbers and use only elementary combinatorial arguments. \nThis is joint work with Jeremy Alm\, Kayla Coffey\, and Carolyn Langhoff.
URL:https://dimag.ibs.re.kr/event/2021-04-13/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210407T170000
DTEND;TZID=Asia/Seoul:20210407T180000
DTSTAMP:20260418T001727
CREATED:20210301T235812Z
LAST-MODIFIED:20240705T190042Z
UID:3701-1617814800-1617818400@dimag.ibs.re.kr
SUMMARY:Michał Pilipczuk\, Structural properties of powers of sparse graphs
DESCRIPTION:For a graph G and an integer d\, the dth power of G is the graph $G^d$ on the same vertex set as G where two vertices are considered adjacent if and only if they are at distance at most d in G. Assuming that G is sparse\, what can we say about the structure in $G^d$? Certainly $G^d$ can be dense\, as the square of a star is a complete graph\, but $G^d$ still retains many properties that can be derived from the sparsity of G. We will present some recent results in this spirit\, in particular connected to colorings and to the Erdős-Hajnal property\, assuming that G is drawn from a fixed class of bounded expansion or from a fixed nowhere dense class. The talk will be based on the recent papers: “Clustering Powers of Sparse Graphs” (with J. Nešetřil\, P. Ossona de Mendez\, and X. Zhu) and “Erdős-Hajnal properties for powers of sparse graphs” (with M. Briański\, P. Micek\, and M. Seweryn).
URL:https://dimag.ibs.re.kr/event/2021-04-07/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210406T163000
DTEND;TZID=Asia/Seoul:20210406T173000
DTSTAMP:20260418T001727
CREATED:20210308T061306Z
LAST-MODIFIED:20240705T190041Z
UID:3731-1617726600-1617730200@dimag.ibs.re.kr
SUMMARY:Rutger Campbell\, Matroid orientability and representability
DESCRIPTION:In this talk we will have a brief introduction to oriented matroids and their relation to real-representability.
URL:https://dimag.ibs.re.kr/event/2021-04-06/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210401T100000
DTEND;TZID=Asia/Seoul:20210401T110000
DTSTAMP:20260418T001727
CREATED:20210218T001134Z
LAST-MODIFIED:20240705T191014Z
UID:3642-1617271200-1617274800@dimag.ibs.re.kr
SUMMARY:Sophie Spirkl\, Pure pairs in ordered graphs
DESCRIPTION:A pure pair in a graph G is a pair of subsets A\, B of the vertex set of G such that in G\, either all of the edges or none of the edges between A and B are present. Pure pairs have been studied recently motivated by their connections to the Erdos-Hajnal conjecture. \nIn this talk\, I will discuss the topic of pure pairs in ordered graphs\, that is\, graphs with a linear ordering on their vertex set. If we exclude a graph H as an ordered induced subgraph\, how large a pure pair can we guarantee? I will talk about how the answer differs from the case of unordered graphs and show some of the techniques used. \nBased on joint work with Maria Chudnovsky\, Jacob Fox\, Alex Scott\, and Paul Seymour.
URL:https://dimag.ibs.re.kr/event/2021-04-01/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210330T163000
DTEND;TZID=Asia/Seoul:20210330T173000
DTSTAMP:20260418T001727
CREATED:20210225T090612Z
LAST-MODIFIED:20240707T081638Z
UID:3676-1617121800-1617125400@dimag.ibs.re.kr
SUMMARY:Casey Tompkins\, 3-uniform hypergraphs avoiding a cycle of length four
DESCRIPTION:We show that that the maximum number of of edges in a $3$-uniform hypergraph without a Berge-cycle of length four is at most $(1+o(1)) \frac{n^{3/2}}{\sqrt{10}}$. This improves earlier estimates by Győri and Lemons and by Füredi and Özkahya. Joint work with Ergemlidze\, Győri\, Methuku\, Salia.
URL:https://dimag.ibs.re.kr/event/2021-03-30/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210324T170000
DTEND;TZID=Asia/Seoul:20210324T180000
DTSTAMP:20260418T001727
CREATED:20210219T024236Z
LAST-MODIFIED:20240705T191012Z
UID:3649-1616605200-1616608800@dimag.ibs.re.kr
SUMMARY:Édouard Bonnet\, Twin-width and ordered binary structures
DESCRIPTION:The twin-width of a graph G can be defined as the least integer d such that there is a sequence of length |V(G)| of (strictly) coarser and coarser partitions of its vertex set V(G)\, and every part X of every partition P of the sequence has at most d other parts Y of P with both at least one edge and at least one non-edge between X and Y.  Twin-width is closely tied to total orders on the vertices\, and can be extended to general binary structures. We will thus consider the twin-width of ordered binary structures\, or if you prefer\, matrices on a finite alphabet. This turns out to be key in understanding combinatorial\, algorithmic\, and model-theoretic properties of (hereditary) classes of those objects. We will see several characterizations of bounded twin-width for these classes. The main consequences in the three domains read as follows. \n\nEnumerative combinatorics: All the classes of 0\,1-matrices with superexponential growth have growth at least n! (in turn resolving a conjecture of Balogh\, Bollobás\, and Morris on the growth of hereditary classes of ordered graphs).\nAlgorithms: First-order model checking of ordered binary structures is tractable exactly when the twin-width is bounded.\nFinite model theory: Monadically-dependent and dependent hereditary classes of ordered binary structures are the same.\n\nIn addition we get a fixed-parameter algorithm approximating matrix twin-width within a function of the optimum\, which is still missing for unordered graphs. \nJoint work with Ugo Giocanti\, Patrice Ossona de Mendez\, and Stéphan Thomassé. Similar results have been obtained independently by Pierre Simon and Szymon Toruńczyk.
URL:https://dimag.ibs.re.kr/event/2021-03-24/
LOCATION:Zoom ID: 869 4632 6610 (ibsdimag)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210322T163000
DTEND;TZID=Asia/Seoul:20210322T173000
DTSTAMP:20260418T001727
CREATED:20210307T042041Z
LAST-MODIFIED:20240705T190041Z
UID:3721-1616430600-1616434200@dimag.ibs.re.kr
SUMMARY:Hong Liu (刘鸿)\, Nested cycles with no geometric crossing
DESCRIPTION:In 1975\, Erdős asked the following question: what is the smallest function $f(n)$ for which all graphs with $n$ vertices and $f(n)$ edges contain two edge-disjoint cycles $C_1$ and $C_2$\, such that the vertex set of $C_2$ is a subset of the vertex set of $C_1$ and their cyclic orderings of the vertices respect each other? We prove the optimal linear bound $f(n)=O(n)$ using sublinear expanders. \nThis is joint work with Irene Gil Fernández\, Jaehoon Kim and Younjin Kim.
URL:https://dimag.ibs.re.kr/event/2021-03-22/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210317T170000
DTEND;TZID=Asia/Seoul:20210317T180000
DTSTAMP:20260418T001727
CREATED:20210228T115822Z
LAST-MODIFIED:20240705T190042Z
UID:3692-1616000400-1616004000@dimag.ibs.re.kr
SUMMARY:Yixin Cao (操宜新)\, Recognizing (unit) interval graphs by zigzag graph searches
DESCRIPTION:Corneil\, Olariu\, and Stewart [SODA 1998; SIAM Journal on Discrete Mathematics 2009] presented a recognition algorithm for interval graphs by six graph searches. Li and Wu [Discrete Mathematics & Theoretical Computer Science 2014] simplified it to only four. The great simplicity of the latter algorithm is however eclipsed by the complicated and long proofs. The main purpose of this paper is to present a new and significantly shorter proof for Li and Wu’s algorithm\, as well as a simpler implementation. We also give a self-contained presentation of the recognition algorithm of Corneil [Discrete Applied Mathematics 2004] for unit interval graphs\, based on three sweeps of graph searches. Moreover\, we show that two sweeps are already sufficient. Toward the proofs of the main results\, we make several new structural observations that might be of independent interests.
URL:https://dimag.ibs.re.kr/event/2021-03-17/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Virtual Discrete Math Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20210316T163000
DTEND;TZID=Asia/Seoul:20210316T173000
DTSTAMP:20260418T001727
CREATED:20210304T000046Z
LAST-MODIFIED:20240705T190041Z
UID:3717-1615912200-1615915800@dimag.ibs.re.kr
SUMMARY:Se-Young Yun (윤세영)\, Regret in Online Recommendation Systems
DESCRIPTION:We propose a theoretical analysis of recommendation systems in an online setting\, where items are sequentially recommended to users over time. In each round\, a user\, randomly picked from a population of m users\, requests a recommendation. The decision-maker observes the user and selects an item from a catalogue of n items. Importantly\, an item cannot be recommended twice to the same user. The probabilities that a user likes each item are unknown. The performance of the recommendation algorithm is captured through its regret\, considering as a reference an Oracle algorithm aware of these probabilities. We investigate various structural assumptions on these probabilities: we derive for each structure regret lower bounds\, and devise algorithms achieving these limits. Interestingly\, our analysis reveals the relative weights of the different components of regret: the component due to the constraint of not presenting the same item twice to the same user\, that due to learning the chances users like items\, and finally that arising when learning the underlying structure. \nThis is joint work with Kaito Ariu\, Narae Ryu\, and Alexandre Proutière.
URL:https://dimag.ibs.re.kr/event/2021-03-16/
LOCATION:Room B232\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
END:VCALENDAR