October 2022

Florent Koechlin, Uniform random expressions lack expressivity

Room B332 IBS (기초과학연구원)

In computer science, random expressions are commonly used to analyze algorithms, either to study their average complexity, or to generate benchmarks to test them experimentally. In general, these approaches only consider the expressions as purely syntactic trees, and completely ignore their semantics — i.e. the mathematical object represented by the expression. However, two different expressions

Dabeen Lee (이다빈), Non-smooth and Hölder-smooth submodular optimization

Room 1501, Bldg. E6-1, KAIST

We study the problem of maximizing a continuous DR-submodular function that is not necessarily smooth. We prove that the continuous greedy algorithm achieves an guarantee when the function is monotone and Hölder-smooth, meaning that it admits a Hölder-continuous gradient. For functions that are non-differentiable or non-smooth, we propose a variant of the mirror-prox algorithm that

November 2022

Jungho Ahn (안정호), Unified almost linear kernels for generalized covering and packing problems on nowhere dense classes

Room B332 IBS (기초과학연구원)

Let $\mathcal{F}$ be a family of graphs, and let $p$ and $r$ be nonnegative integers. The $(p,r,\mathcal{F})$-Covering problem asks whether for a graph $G$ and an integer $k$, there exists a set $D$ of at most $k$ vertices in $G$ such that $G^p\setminus N_G^r$ has no induced subgraph isomorphic to a graph in $\mathcal{F}$, where

Hugo Jacob, On the parameterized complexity of computing tree-partitions

Zoom ID: 869 4632 6610 (ibsdimag)

Following some recent FPT algorithms parameterized by the width of a given tree-partition due to Bodlaender, Cornelissen, and van der Wegen, we consider the parameterized problem of computing a decomposition. We prove that computing an optimal tree-partition is XALP-complete, which is likely to exclude FPT algorithms. However, we prove that computing a tree-partition of approximate

Sebastian Wiederrecht, Excluding single-crossing matching minors in bipartite graphs

Room B332 IBS (기초과학연구원)

By a seminal result of Valiant, computing the permanent of (0, 1)-matrices is, in general, #P-hard. In 1913 Pólya asked for which (0, 1)-matrices A it is possible to change some signs such that the permanent of A equals the determinant of the resulting matrix. In 1975, Little showed these matrices to be exactly the

Chong Shangguan (上官冲), On the sparse hypergraph problem of Brown, Erdős and Sós

Zoom ID: 224 221 2686 (ibsecopro)

For fixed integers $r\ge 3, e\ge 3$, and $v\ge r+1$, let $f_r(n,v,e)$ denote the maximum number of edges in an $n$-vertex $r$-uniform hypergraph in which the union of arbitrary $e$ distinct edges contains at least $v+1$ vertices. In 1973, Brown, Erdős and Sós initiated the study of the function $f_r(n,v,e)$ and they proved that $\Omega(n^{\frac{er-v}{e-1}})=f_r(n,v,e)=O(n^{\lceil\frac{er-v}{e-1}\rceil})$.

Seonghyuk Im (임성혁), A proof of the Elliott-Rödl conjecture on hypertrees in Steiner triple systems

Room B332 IBS (기초과학연구원)

A linear $3$-graph is called a (3-)hypertree if there exists exactly one path between each pair of two distinct vertices.  A linear $3$-graph is called a Steiner triple system if each pair of two distinct vertices belong to a unique edge. A simple greedy algorithm shows that every $n$-vertex Steiner triple system $G$ contains all

The 2nd Workshop on Developments in Combinatorics

Zoom ID: 346 934 4087 (202209)

Official website (with the abstract) https://www.ibs.re.kr/ecopro/online-workshop-developments-in-combinatorics/ Invited Speakers Nov. 28 Monday Jie Han, Beijing Institute of Technology 15:30 Seoul, 14:30 Beijing, 06:30 UK, 07:30 EU Joonkyung Lee (이준경), Hanyang University 16:10 Seoul, 15:10 Beijing, 07:10 UK, 08:10 EU Lior Gishboliner, ETH Zürich 16:50 Seoul, 15:50 Beijing, 07:50 UK, 08:50 EU Alex Scott, University of Oxford

December 2022

Cosmin Pohoata, Convex polytopes from fewer points

Zoom ID: 224 221 2686 (ibsecopro)

Finding the smallest integer $N=ES_d(n)$ such that in every configuration of $N$ points in $\mathbb{R}^d$ in general position, there exist $n$ points in convex position is one of the most classical problems in extremal combinatorics, known as the Erdős-Szekeres problem. In 1935, Erdős and Szekeres famously conjectured that $ES_2(n)=2^{n−2}+1$ holds, which was nearly settled by

Giannos Stamoulis, Model-Checking for First-Order Logic with Disjoint Paths Predicates in Proper Minor-Closed Graph Classes

Room B332 IBS (기초과학연구원)

The disjoint paths logic, FOL+DP,  is an extension of First Order Logic (FOL) with the extra atomic predicate $\mathsf{dp}_k(x_1,y_1,\ldots,x_k,y_k),$ expressing the existence of internally vertex-disjoint paths between $x_i$ and $y_i,$ for $i\in \{1,\ldots, k\}$. This logic can express a wide variety of problems that escape the expressibility potential of FOL. We prove that for every

기초과학연구원 수리및계산과학연구단 이산수학그룹
대전 유성구 엑스포로 55 (우) 34126
IBS Discrete Mathematics Group (DIMAG)
Institute for Basic Science (IBS)
55 Expo-ro Yuseong-gu Daejeon 34126 South Korea
E-mail: dimag@ibs.re.kr, Fax: +82-42-878-9209