879 research outputs found
Graph multicoloring reduction methods and application to McDiarmid-Reed's Conjecture
A -coloring of a graph associates to each vertex a set of
colors from a set of colors in such a way that the color-sets of adjacent
vertices are disjoints. We define general reduction tools for -coloring
of graphs for . In particular, we prove necessary and sufficient
conditions for the existence of a -coloring of a path with prescribed
color-sets on its end-vertices. Other more complex -colorability
reductions are presented. The utility of these tools is exemplified on finite
triangle-free induced subgraphs of the triangular lattice. Computations on
millions of such graphs generated randomly show that our tools allow to find
(in linear time) a -coloring for each of them. Although there remain few
graphs for which our tools are not sufficient for finding a -coloring,
we believe that pursuing our method can lead to a solution of the conjecture of
McDiarmid-Reed.Comment: 27 page
Extended core and choosability of a graph
A graph is -choosable if for any color list of size associated
with each vertices, one can choose a subset of colors such that adjacent
vertices are colored with disjoint color sets. This paper shows an equivalence
between the -choosability of a graph and the -choosability of one
of its subgraphs called the extended core. As an application, this result
allows to prove the -choosability and -colorability of
triangle-free induced subgraphs of the triangular lattice.Comment: 10 page
Choosability of a weighted path and free-choosability of a cycle
A graph with a list of colors and weight for each vertex
is -colorable if one can choose a subset of colors from
for each vertex , such that adjacent vertices receive disjoint color
sets. In this paper, we give necessary and sufficient conditions for a weighted
path to be -colorable for some list assignments . Furthermore, we
solve the problem of the free-choosability of a cycle.Comment: 9 page
Vectorial solutions to list multicoloring problems on graphs
For a graph with a given list assignment on the vertices, we give an
algebraical description of the set of all weights such that is
-colorable, called permissible weights. Moreover, for a graph with a
given list and a given permissible weight , we describe the set of all
-colorings of . By the way, we solve the {\sl channel assignment
problem}. Furthermore, we describe the set of solutions to the {\sl on call
problem}: when is not a permissible weight, we find all the nearest
permissible weights . Finally, we give a solution to the non-recoloring
problem keeping a given subcoloring.Comment: 10 page
Jacques Benoît, Jos Carbone, Montréal, Éditions du Jour, « Les Romanciers du jour », 1967, 120 p.
SIMARD, François-Xavier et André LA ROSE, Jean Despréz (1906-1965). Une femme de tête, de courage et de coeur, Ottawa, Éditions du Vermillon, 2001
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