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Theses

Proper and weak-proper trees in edges-colored graphs and multigraphs

Abstract : In this thesis, we investigate the extraction of trees from edge-colored graphs. We focus on finding trees with properties based on coloring. Namely, we deal with proper and weak proper spanning trees, denoted PST and WST.- We show the optimization versions of these problems to be NP-hard in the general case of edge-colored graphs and we provide algorithms to find these trees in the case of edge-colored graphs without properly edge-colored cycles. We also provide some nonapproximability bounds.- We investigate the existence of a PST in the case of edge-colored graphs under certain conditions on the graph, both structural and related to the coloration. We consider sufficient conditions that guarantee the existence of a PST in edge-colored (not necessarily proper) graphs with any number of colors. The conditions we consider are combinations ofvarious parameters such as : total number of colors, number of vertices, connectivity and the number of incident edges of different colors to the vertices.- We then consider properly edge-colored Hamiltonian paths in the edge-colored multigraphs, which are relevant to our study since they are also PST. We establish sufficient conditions for a multigraph to contain a proper edge-colored Hamiltonian path, depending on several parameters such as the number of edges, the degree of edges, etc.- Since one of the sufficient conditions for the existence of proper spanning trees is connectivity, we prove several upper bounds for the smallest number of colors needed to color a graph such that it is k-proper-connected. We state several conjectures for general and bipartite graphs, and we prove them for k = 1.
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Valentin Borozan. Proper and weak-proper trees in edges-colored graphs and multigraphs. Other [cs.OH]. Université Paris Sud - Paris XI, 2011. English. ⟨NNT : 2011PA112165⟩. ⟨tel-00738959⟩

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