INRIA project-team GANG

Thematic team Theory and algorithmics of graphs

## Graphs

#### Day, hour and place

#### Contact(s)

### Previous talks

#### Year 2019

Graphs

Tuesday April 9, 2019, 2PM, Salle 3052

**Binh-Minh Bui-Xuan** (LIP6) *Temporal matching*

In contrast to classical graph theory, we show that the problem of computing a temporal matching of maximum size in a link stream is in general NP-hard. We then depict a kernelization algorithm parameterized by the solution size for the problem, producing quadratic kernels. As a byproduct we also give a 2-approximation algorithm. Both algorithms are implemented and confronted to link streams collected from real world graph data:

https://github.com/antoinedimitriroux/Temporal-Matching-in-Link-Streams

We observe from the experiments that the kernelization algorithm can perform very well in practice, reducing the instance size downto 10-20% on realistic mining parameters. In contrast, the 2-approximation gives rather mixed results. We conjecture that the approximation factor can be improved.

Graphs

Friday March 22, 2019, 2PM, Salle 1007

**Julien Baste** (Universität Ulm, Ulm, Germany) *Hitting minors on bounded treewidth graphs*

The presented results are joint work with Ignasi Sau and Dimitrios Thilikos and can be found in <https://arxiv.org/abs/1704.07284>.

Graphs

Tuesday March 12, 2019, 2PM, Salle 3052

**Rémy Belmonte** *Token Sliding on Split Graphs*

Joint work with Eun-Jung Kim, Michael Lampis, Valia Mitsou, Yota Otachi and Florian Sikora.

Graphs

Wednesday March 6, 2019, 11AM, Salle 3052

**Marc Lelarge** (Inria & ENS Paris) *Spectral embedding for graph classification*

Although our SGE is handcrafted, we also show how our generic embedding technique can be learned and built in a data-driven manner opening the way to new learning algorithms and deep learning architectures with some invariant constraints built-in.

Graphs

Tuesday February 19, 2019, 2PM, Salle 1007

**Marthe Bonamy** (CNRS - LABRI) *Around Brooks' theorem*

Graphs

Tuesday February 19, 2019, 11AM, Salle 3052

**Danupon Nanongkai** (KTH) *Distributed Shortest Paths, Exactly*

Graphs

Tuesday January 22, 2019, 2PM, Salle 3052

**Guillaume Ducoffe** (ICI Roumanie) *Computing Giant Diameters with Breadth-First Search and Range Queries*

#### Year 2018

Graphs

Tuesday December 18, 2018, 3:30PM, Salle 3052

**Bergougnoux Benjamin** (IRIF) *Rank Based Approach on Graphs with Structured Neighborhood*

The $d$-neighbor equivalence is a tools introduced by Bui-Xuan et al. in 2013 to obtained efficient parameterized algorithms for many width measures (clique-width, rank-width, mim-width,…) and for many problems with a locally checkable constraint (Dominating Set, Independent Set,…).

By combining these two notions, we obtain efficient algorithms for several connectivity problems such as Connected Dominating Set, Node Weighted Steiner Tree, Maximum Induced Tree, Longest Induced Path, and Feedback Vertex Set. For all these problems, we obtain $2^{O(k)}\cdot n^{O(1)}$, $2^{O(k \log(k))}\cdot n^{O(1)}$, $2^{O(k^2)}\cdot n^{O(1)}$ and $n^{O(k)}$ time algorithms parameterized respectively by clique-width, $\mathbb{Q}$-rank-width, rank-width and maximum induced matching width. Our approach simplifies and unifies the known algorithms for each of the parameters and match asymptotically also the best time complexity for Vertex Cover and Dominating Set.

Paper available on HAL : https://hal.archives-ouvertes.fr/hal-01799573v2/document

Graphs

Tuesday December 11, 2018, 2PM, Salle 3052

**Riste Škrekovski** (University of Ljubljana) *Some results and problems on unique-maximum colorings of plane graphs*

We first show that the conjecture holds for various subclasses of planar graphs but then we disprove it for planar graphs in general. So, we conclude that the facial unique-maximum chromatic number of the sphere is not four but five.

Additionally, we will consider a facial edge-coloring analogue of the aforementioned coloring, and we will conclude the talk with various open problems.

(Joint work with Vesna Andova, Bernard Lidick\'y, Borut Lu\v{z}ar, and Kacy Messerschmidt)

Graphs

Thursday November 29, 2018, 2PM, Salle 3014

**Carenne Ludeña** (Universidad Jose Tadeo Lozano) *A random graph model based on the Modular decomposition of graphs*

Graphs

Tuesday November 27, 2018, 2PM, Salle 3052

**Miguel Mendez** *Set operads and decomposition theory*

Graphs

Tuesday October 23, 2018, 2PM, Salle 3052

**Yllka Velaj** (CWI Amsterdam) *Stable Outcomes in Modified Fractional Hedonic Games*

We are interested in the scenario in which agents, individually or jointly, choose to form a new coalition or to join an existing one, until a stable outcome is reached. To this aim, we consider common stability notions, leading to strong Nash stable outcomes, Nash stable outcomes or core stable outcomes: we study their existence, complexity and performance, both in the case of general weights and in the case of 0-1 weights.

Graphs

Tuesday May 22, 2018, 2PM, Salle 1007

**François Pirot** (Université de Strasbourg) *Fractional chromatic number of small degree graphs and girth.*

Graphs

Friday April 6, 2018, 10AM, Salle 3052

**Cédric Bentz** *Steiner trees with edge capacities.*

Graphs

Tuesday April 3, 2018, 2PM, Salle 1007

**Marcin Kaminski** *Induced minors and well-quasi-ordering*

We show that the class of H-free graphs is well-quasi-ordered by induced minors if and only if H is an induced minor of the gem (=the path on 4 vertices plus a dominating vertex) or the graph obtained by adding a vertex of degree 2 to the K4 (= the complete graph on 4 vertices).

This generalizes a a result of Robin Thomas who proved that K4-free graphs are well-quasi-ordered by induced minors and complements similar dichotomy theorems proved by Guoli Ding for subgraphs and Peter Damaschke for induced subgraphs.

This is joint work with Jarosław Błasiok, Jean-Florent Raymond, and Théophile Trunck.

Graphs

Tuesday March 27, 2018, 2PM, Salle 1007

**Matej Stehlik** (Université Grenoble Alpes - GSCOP) *Nombre chromatique et la méthode topologique*

Graphs

Tuesday March 20, 2018, 2PM, Salle 1007

**Pierluigi Crescenzi** (Universite de Pise) *Computing node centrality in large graphs: from theory to practice and back*

Graphs

Tuesday March 13, 2018, 2PM, Salle 1007

**Mamadou Kante** (ISIMA) *Obstructions pour certaines classes de matroides linéaires*

Graphs

Tuesday February 27, 2018, 2PM, Salle 1007

**Dieter Mitsche** (Université Nice) *Aspects des Graphes Aléatoires*

Graphs

Tuesday February 20, 2018, 2PM, Salle 1007

**Jan Arne Telle** (University of Bergen) *Width parameters of graphs and structured graph classes*

Parts of the talk are based on joint work with O.Kwon and L.Jaffke, to appear at STACS 2018.

Graphs

Monday February 12, 2018, 2PM, Salle 3052

**Nabil Mustafa** (ESIEE) *Local Search for Geometric Optimization Problems.*

#### Year 2017

Graphs

Tuesday December 12, 2017, 2PM, Salle 3052

**Jean Krivine** (IRIF) *Incremental Update for Graph Rewriting*

Reference: Boutillier P., Ehrhard T., Krivine J. (2017) Incremental Update for Graph Rewriting. In: Yang H. (eds) Programming Languages and Systems. ESOP 2017. Lecture Notes in Computer Science, vol 10201. Springer, Berlin, Heidelberg

Graphs

Tuesday October 17, 2017, 2PM, Salle 3052

**Claire Mathieu** (DI - ENS) *Online k-compaction*

This is joint work with Carl Staelin, Neal E. Young, and Arman Yousefi.