{"id":92,"date":"2021-06-23T17:34:52","date_gmt":"2021-06-23T15:34:52","guid":{"rendered":"https:\/\/project.inria.fr\/anrdigraphs\/?page_id=92"},"modified":"2023-06-06T19:56:44","modified_gmt":"2023-06-06T17:56:44","slug":"meetings","status":"publish","type":"page","link":"https:\/\/project.inria.fr\/anrdigraphs\/meetings\/","title":{"rendered":"Meetings"},"content":{"rendered":"

<\/h3>\n

<\/h3>\n

Fifth ANR Digraph meeting<\/h3>\n

S\u00e8te May 30 – June 2, 2023.<\/h4>\n

Participants: <\/b>
Pierre Aboulker, Guillaume Aubian, Joergen Bang-Jensen, <\/span>St\u00e9phane Bessy, Romain Biourneuf, Pierre Charbit, <\/span>Julien Duron, Colin Geniet, <\/span>Emeric Gioan, <\/span>Daniel Gon\u00e7alves, Ararat Harutyunyan, <\/span>Fr\u00e9d\u00e9ric Havet, Florian Hoersch, Hugo Jacob, Kolja Knauer, William Lochet, <\/span>Yann Marin,<\/span> Lucas Picasarri-Arrieta, Gil Puigi-Surroca<\/span>, <\/span>Cl\u00e9ment Rambaud, <\/span>Amadeus Reinald, St\u00e9phan Thomass\u00e9, <\/span>Nicolas Trotignon, Petru Valicov, <\/span><\/span>R\u00e9mi Watrigant, Raul Wayne, Anders Yeo
\n<\/span><\/p>\n

Programme :<\/b><\/span><\/h4>\n


\nMardi<\/span> 30 Mai
\n————————————————-
\n9h30-10h30 Joergen Bang-Jensen : Open problem in digraphs. Slides<\/a><\/span><\/p>\n

10h45-12h00 Open Problems Session 1.
\n————————————————-
\n14h00-15h00 Open Problems Session 2.\u00a0 Open Problems of the 2 sessions<\/a><\/span><\/p>\n

15h15-15h50 Raul Lopes :\u00a0 New Menger-like dualities in digraphs and applications to half-integral linkages.<\/span><\/p>\n

Mercredi<\/span> 31 Mai
\n————————————————-
\n9h30-10h30 Anders Yeo : Directed max-cut and some generalizations. Slides<\/a>
\n10h45-11h25 Guillaume Aubian : Maximum local arc-connectivity and dichromatic number. Slides<\/a>
\n11h30-12h15 Julien Duron : On the minimum number of inversions to make a digraph k-(arc-)strong. Slides<\/a><\/p>\n

————————————————-<\/span><\/p>\n

14h30-15h00 Yann Marin : Oriented matroid convexity in directed graphs.
\n<\/span><\/p>\n

Jeudi<\/span> 1er Juin
\n————————————————-<\/span><\/p>\n

9h45-10h30 Colin Geniet : A tamed family of triangle-free graphs with unbounded chromatic number
\n10h45-11h15 Lucas Picasarri-Arrieta : On the minimum number of arcs in 4-dicritical oriented graphs. Slides<\/a>
\n11h20-12h00: Gil Puigi-Surroca<\/span> : Dichromatic number\/list number of some families of digraphs. Slides<\/a><\/p>\n

Vendredi<\/span> 2 Juin
\n————————————————<\/p>\n

10h00 : Solved\u00a0 problems.
\n<\/span><\/p>\n

<\/b>
\n<\/span><\/p>\n

<\/h3>\n

Fourth ANR Digraph meeting<\/h3>\n

Lyon January 25 – 27, 2023.<\/h4>\n
Participants: <\/b>
Pierre Aboulker, Guillaume Aubian, <\/span>St\u00e9phane Bessy, <\/span>Julien Duron, Colin Geniet, <\/span>Emeric Gioan, <\/span>Daniel Gon\u00e7alves, <\/span>Fr\u00e9d\u00e9ric Havet, <\/span>Yann Marin, <\/span>Nicolas Nisse, Lucas Picasarri-Arrieta, <\/span>Pegah Pournajafi, <\/span>Cl\u00e9ment Rambaud, <\/span>Amadeus Reinald, St\u00e9phna Thomass\u00e9, <\/span>Nicolas Trotignon, <\/span><\/span>R\u00e9mi Watrigant

\n<\/b><\/span><\/div>\n
<\/div>\n
Programme : <\/b><\/span><\/div>\n
A partir de 9:00 : accueil caf\u00e9, discussion libre<\/span><\/div>\n
<\/div>\n
10:00 – 11:30 : s\u00e9ance de probl\u00e8mes ouverts<\/strong>,\u00a0 pr\u00e9sence de tous attendu\u00a0<\/span><\/div>\n
<\/div>\n
11:30 : d\u00e9jeuner
\n<\/span><\/div>\n
<\/div>\n
13:30 – 14:30 Ramsey Problem for the dichromatic number<\/strong><\/span><\/div>\n
Par Pierre Aboulker<\/span><\/div>\n
<\/div>\n
15:00 – 18:00 Suite des probl\u00e8mes ouverts, travail en groupe<\/span><\/div>\n
<\/div>\n
Jeudi\u00a0<\/b><\/span><\/div>\n
<\/div>\n
10:00 <\/span>P<\/span>rogr\u00e8s sur les inversions\u00a0<\/span><\/strong><\/div>\n
Par Cl\u00e9ment Rambaud<\/span><\/div>\n
<\/div>\n
11:30 D\u00e9jeuner<\/span><\/div>\n
<\/div>\n
13:30 : Probl\u00e8mes ouverts puis travail en groupe<\/span><\/div>\n
<\/div>\n
<\/div>\n
Vendredi<\/b><\/span><\/div>\n
<\/div>\n
10:00 Reconfigurations de dicolorations.<\/strong><\/span><\/div>\n
Par Lucas Picasarri-Arrieta<\/span><\/div>\n
<\/div>\n
11:30 D\u00e9jeuner<\/span><\/div>\n
<\/div>\n
13:30: Travail en groupe<\/span>
\n<\/span><\/div>\n
<\/div>\n
<\/div>\n

Third ANR Digraph meeting<\/h3>\n

Les Plantiers June 27 – July 3, 2022.<\/h4>\n

Participants: <\/b>
Pierre Aboulker, Guillaume Aubian, <\/span>Pierre Charbit, <\/span>Julien Duron, Colin Geniet, <\/span>Emeric Gioan<\/span>, Ararat Harutyunyan, <\/span>Fr\u00e9d\u00e9ric Havet, Florian Hoersch, Felix Klingelhoefer<\/span>, William Lochet, <\/span>Alantha Newman, Nicolas Nisse, Lucas Picasarri-Arrieta,<\/span> Cl\u00e9ment Rambaud,<\/span> St\u00e9phan Thomass\u00e9, Quentin Vermande<\/span>.
\n<\/span><\/p>\n

<\/h3>\n

Second ANR Digraph meeting<\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 on-line June 15 – 18, 2021.<\/h4>\n

Programme :<\/strong><\/h5>\n

Tuesday June 15<\/strong><\/p>\n

2pm<\/strong> : Fr\u00e9d\u00e9ric Havet, Dichromatic number of surfaces.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>Pr\u00e9sentation<\/a><\/p>\n

Abstract: The dichromatic number of a surface is the maximum dichromatic number of an oriented graph embedded in that surface. We give asymptotic bounds on the dichromatic number of a surface, and compute its exact value for some particular surfaces.<\/em>
\nThis is a joint work with Pierre Aboulker, Kolja Knauer, and Cl\u00e9ment Rambaud.<\/em><\/p>\n

3 pm<\/strong> : Fr\u00e9d\u00e9ric Havet, Inversion in tournaments.\u00a0\u00a0\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 <\/strong>\u00a0Pr\u00e9sentation<\/a><\/p>\n

Abstract: Let D be an oriented graph. The inversion of a set X of vertices in D consists in reversing the direction of all arcs with both ends in X. The inversion number of D, denoted by inv(D), is the minimum number of inversions needed to make D acyclic. Denoting by tau(D), tau’ (D), and nu(D) the cycle transversal number, the cycle arc-transversal number and the cycle packing number of D respectively, one shows that inv(D) <= tau’ (D), inv(D) <= 2.tau(D) and there exists a function g such that inv(D)<= g(nu(D)).<\/em>
\nWe conjecture that for any two oriented graphs L and R, inv(L ra R) =inv(L) +inv(R) where L ra R is the dijoin of L and R. This would imply that the first two inequalities are tight. We prove this conjecture when inv(L)<= 1 and inv(R)<= 2 and when inv(L) =inv(R)=2 and L and R are strongly connected. We also show that the function g of the third inequality satisfies g(1)<= 4.<\/em><\/p>\n

\n

Wednesday June 16<\/strong><\/p>\n

2 pm<\/strong> : Pegah Pournajafi, Burling graphs revisited.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>Pr\u00e9sentation<\/a><\/p>\n

Abstract: The Burling graphs form a class of triangle-free graphs with unbounded chromatic number. This class has attracted some attention because of its geometric representation and its importance in studying questions about chromatic number in hereditary classes of graphs. In this talk, we introduce some equivalent definitions of Burling graphs and then explain how one of these definitions can help us to find information about the structure of the graphs in this class.<\/em>
\nThis talk is based on joint work with Nicolas Trotignon. Some results are from https:\/\/arxiv.org\/abs\/2104.07001.<\/em><\/p>\n

\n

3 pm<\/strong> : Edouard Bonnet, Twin-width pour les graphes orient\u00e9s.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>Pr\u00e9sentation<\/a><\/p>\n

Abstract: La twin-width pour les graphes orient\u00e9s est similaire \u00e0 la twin-width ‘usuelle’ mais il y a des questions propres aux graphes orient\u00e9s. Par ex: est-il vrai que pour les tournois la tww born\u00e9e correspond exactement \u00e0 FO model checking en temps FPT? Ou encore comment se fait-il que les graphes extr\u00e9maux de CH, la conjecture qui ne doit pas \u00eatre nomm\u00e9e, sont de twin-width born\u00e9e, etc…<\/em><\/p>\n

\n

4<\/strong> pm<\/strong> : Open problems session<\/strong><\/p>\n

\n

Friday June 18<\/strong><\/p>\n

Abstract: Gyarf\u00e1s-Sumner Conjecture asserts that for every integer k and every forest T, the class of graphs with no clique on k vertices nor induced subgraphs isomorphic to T have bounded chromatic number. We will investigate an analogue of this conjecture for oriented graphs.<\/em>
\nThis is a joint work with Pierre Charbit and Reza Naserasr.<\/em><\/p>\n

\n

10:30 am<\/strong>\u00a0 : Guillaume Aubian, Decomposition theorem for locally in-transitive tournaments.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>Pr\u00e9sentation<\/a>
\nAbstract: A tournament is an orientation of a complete graph. A transitive tournament is an acylic tournament. An oriented graph is in-locally transitive if the in-neighborhood of each vertex is a transitive tournament.<\/em>
\nWe give a decomposition theorem for the class of locally in-transitive tournaments. As a consequence we obtain several applications, among which an answer to a Conjecture of Aboulker, Charbit and Naserasr about the dichromatic number, as well as a proof of the Caccetta\u2013H\u00e4ggkvist conjecture for this class.<\/em>
\nThis is a joint work with Pierre Aboulker and Pierre Charbit.<\/em><\/p>\n

\n

First ANR Digraph meeting<\/h3>\n

Seguret January 22 – 24, 2020.<\/h4>\n","protected":false},"excerpt":{"rendered":"

Fifth ANR Digraph meeting S\u00e8te May 30 – June 2, 2023. Participants: Pierre Aboulker, Guillaume Aubian, Joergen Bang-Jensen, St\u00e9phane Bessy, Romain Biourneuf, Pierre Charbit, Julien Duron, Colin Geniet, Emeric Gioan, Daniel Gon\u00e7alves, Ararat Harutyunyan, Fr\u00e9d\u00e9ric Havet, Florian Hoersch, Hugo Jacob, Kolja Knauer, William Lochet, Yann Marin, Lucas Picasarri-Arrieta, Gil Puigi-Surroca,\u2026<\/p>\n

Continue reading<\/span><\/i><\/a> <\/p>\n","protected":false},"author":1386,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-92","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/pages\/92","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/users\/1386"}],"replies":[{"embeddable":true,"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/comments?post=92"}],"version-history":[{"count":30,"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/pages\/92\/revisions"}],"predecessor-version":[{"id":160,"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/pages\/92\/revisions\/160"}],"wp:attachment":[{"href":"https:\/\/project.inria.fr\/anrdigraphs\/wp-json\/wp\/v2\/media?parent=92"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

9:30 am<\/strong> : Pierre Aboulker, Analogue of Gy\u00e1rf\u00e1s-Sumner conjecture for oriented graphs.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>Pr\u00e9sentation<\/a><\/p>\n