### Reinhard Diestel, Tangles of set separations: a novel clustering method and type recognition in machine learning

Zoom ID: 934 3222 0374 (ibsdimag)

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

### Raul Lopes, Adapting the Directed Grid Theorem into an FPT Algorithm

Zoom ID: 934 3222 0374 (ibsdimag)

The Grid Theorem of Robertson and Seymour 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. , and proved by Kawarabayashi and Kreutzer .

### Johannes Carmesin, A Whitney type theorem for surfaces: characterising graphs with locally planar embeddings

Zoom ID: 934 3222 0374 (ibsdimag)

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. Our embedding method is based

### Benjamin Bumpus, Directed branch-width: A directed analogue of tree-width

Zoom ID: 934 3222 0374 (ibsdimag)

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’. In this talk,

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