Chromatic Sums for Colorings Avoiding Monochromatic Subgraphs
Discussiones Mathematicae. Graph Theory, Tome 35 (2015) no. 3, pp. 541-555

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Given graphs G and H, a vertex coloring c : V (G) →ℕ is an H-free coloring of G if no color class contains a subgraph isomorphic to H. The H-free chromatic number of G, χ (H,G), is the minimum number of colors in an H-free coloring of G. The H-free chromatic sum of G, ∑(H,G), is the minimum value achieved by summing the vertex colors of each H-free coloring of G. We provide a general bound for ∑(H,G), discuss the computational complexity of finding this parameter for different choices of H, and prove an exact formulas for some graphs G. For every integer k and for every graph H, we construct families of graphs, Gk with the property that k more colors than χ (H,G) are required to realize ∑(H,G) for H-free colorings. More complexity results and constructions of graphs requiring extra colors are given for planar and outerplanar graphs.
Keywords: coloring, sum of colors, forbidden subgraphs
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     author = {Kubicka, Ewa and Kubicki, Grzegorz and McKeon, Kathleen A.},
     title = {Chromatic {Sums} for {Colorings} {Avoiding} {Monochromatic} {Subgraphs}},
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Kubicka, Ewa; Kubicki, Grzegorz; McKeon, Kathleen A. Chromatic Sums for Colorings Avoiding Monochromatic Subgraphs. Discussiones Mathematicae. Graph Theory, Tome 35 (2015) no. 3, pp. 541-555. http://geodesic.mathdoc.fr/item/DMGT_2015_35_3_a11/