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Université de Fribourg

A note on chromatic properties of threshold graphs

Ries, Bernard ; de Werra, Dominique ; Zenklusen, Rico

In: Discrete Mathematics, 2012, vol. 312, no. 10, p. 1838-1843

In threshold graphs one may find weights for the vertices and a threshold value t such that for any subset S of vertices, the sum of the weights is at most the threshold t if and only if the set S is a stable (independent) set. In this note we ask a similar question about vertex colorings: given an integer p, when is it possible to find weights (in general depending on p) for the vertices and a...

Université de Fribourg

Blockers and transversals in some subclasses of bipartite graphs : When caterpillars are dancing on a grid

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

In: Discrete Mathematics, 2010, vol. 310, p. 132-146

Given an undirected graph G=(V,E) with matching number \nu(G), a d-blocker is a subset of edges B such that \nu(/V,E\B))= d. While the associated decision problem is NP-complete in bipartite graphs we show how to construct efficiently minimum d-transversals and minimum d-blockers in the...