Incremental list coloring of graphs, parameterized by conservation

Incrementally k-list coloring a graph means that a graph is given by adding vertices step by step, and for each intermediate step we ask for a vertex coloring such that each vertex has one of the colors specified by its associated list containing some of in total k colors. We introduce the "conservative version" of this problem by adding a further parameter c is an element of N specifying the maximum number of vertices to be recolored between two subsequent graphs (differing by one vertex). The "conservation parameter" c models the natural quest for a modest evolution of the coloring in the course of the incremental process instead of performing radical changes. We show that even on bipartite graphs the problem is NP-hard for k >= 3 and W[1]-hard for an unbounded number of colors when parameterized by c. In contrast, also on general graphs the problem becomes fixed-parameter tractable with respect to the combined parameter (k, c). We prove that the problem has an exponential-size kernel with respect to (k, c) and there is no polynomial-size kernel unless NP subset of coNP/poly. Furthermore, we investigate the parameterized complexity on various subclasses of perfect graphs. We show fixed-parameter tractability for the combined parameter treewidth and number k of colors. Finally, we provide empirical findings on the practical relevance of our approach in terms of an effective graph coloring heuristic. (c) 2013 Elsevier B.V. All rights reserved.