Université de Fribourg

Contraction and deletion blockers for perfect graphs and H-free graphs

Y. Diner, Öznur ; Paulusma, Daniël ; Picouleau, Christophe ; Ries, Bernard

In: Theoretical computer science, 2018, vol. 746, p. 49-72

We study the following problem: for given integers d, k and graph G, can we reduce some fixed graph parameter π of G by at least d via at most k graph operations from some fixed set S? As parameters we take the chromatic number χ, clique number ω and independence number α, and as operations we choose edge contraction ec and vertex deletion vd. We determine the complexity of this problem...

Université de Fribourg

Blockers and transversals

Zenklusen, Rico ; Ries, Bernard ; Picouleau, Christophe ; de Werra, Dominique ; Costa, Marie-Christine ; Bentz, Cédric

In: Discrete Mathematics, 2009, vol. 309, p. 4306-4314

Given an undirected graph G=(V,E) with matching number \nu(G), we define d- blockers as subsets of edges B such that \nu(G=(V,E\B))\leq \nu(G)-d. We define d- transversals T as subsets of edges such that every maximum matching M has |M\cap T|\geq d. We explore connections between d-blockers and d-transversals. Special classes of graphs are examined which include complete graphs, regular...