A Duality Based 2-Approximation Algorithm for Maximum Agreement Forest

We give a 2-approximation algorithm for the Maximum Agreement Forest problem on two rooted binary trees. This NP-hard problem has been studied extensively in the past two decades, since it can be used to compute the Subtree Prune-and-Regraft (SPR) distance between two phylogenetic trees. Our result improves on the very recent 2.5-approximation algorithm due to Shi, Feng, You and Wang (2015). Our algorithm is the first approximation algorithm for this problem that uses LP duality in its analysis

Layers and Matroids for the Traveling Salesman's Paths

Gottschalk and Vygen proved that every solution of the subtour elimination linear program for traveling salesman paths is a convex combination of more and more restrictive "generalized Gao-trees". We give a short proof of this fact, as a layered convex combination of bases of a sequence of increasingly restrictive matroids. A strongly polynomial, combinatorial algorithm follows for finding this convex combination, which is a new tool offering polyhedral insight, already instrumental in recent results for the $s-t$ path TSP

Pour une esthétique du comique : L’Enfant de Jules Vallès

L'article analyse le mode d'emploi du comique vallésien dans L'Enfant. Il montre que Vallès construit son roman sur le principe de l'échappatoire : chaque proposition avancée par le narrateur se ménage toujours une sortie de secours. Cette technique du « faux-fuyant » révèle une esthétique double qui tend simultanément vers la littérature engagée et vers l'autonomie, où le détail inutile tourne en dérision le contenu idéologique. L'ambition de Vallès a été de découvrir un tragique qui soit capable de révéler l'envers grotesque de l'histoire contemporaine

Deterministic Approximation Algorithms for Ranking and Clustering Problems

Deterministic Approximation Algorithms for Ranking and Clustering Problem