3,366 research outputs found
Conjectures on uniquely 3-edge-colorable graphs
A graph is {\it uniquely k-edge-colorable} if the chromatic index of is  and every two -edge-colorings of produce the same partition of into independent subsets.For any , a uniquely -edge-colorable graph is completely characterized; if , is a path or an even cycle if ,and is a star if .On the other hand, there are infinitely many uniquely 3-edge-colorable graphs, and hence, there are many conjectures for the characterization of uniquely 3-edge-colorable graphs.In this paper, we introduce a new conjecture which connects conjectures of uniquely 3-edge-colorable planar graphs with those of uniquely 3-edge-colorable non-planar graphs
Planar graph coloring avoiding monochromatic subgraphs: trees and paths make things difficult
We consider the problem of coloring a planar graph with the minimum number of colors such that each color class avoids one or more forbidden graphs as subgraphs. We perform a detailed study of the computational complexity of this problem
Asymmetric -colorings of graphs
We show that the edges of every 3-connected planar graph except can be
colored with two colors in such a way that the graph has no color preserving
automorphisms. Also, we characterize all graphs which have the property that
their edges can be -colored so that no matter how the graph is embedded in
any orientable surface, there is no homeomorphism of the surface which induces
a non-trivial color preserving automorphism of the graph
Conflict-Free Coloring of Planar Graphs
A conflict-free k-coloring of a graph assigns one of k different colors to
some of the vertices such that, for every vertex v, there is a color that is
assigned to exactly one vertex among v and v's neighbors. Such colorings have
applications in wireless networking, robotics, and geometry, and are
well-studied in graph theory. Here we study the natural problem of the
conflict-free chromatic number chi_CF(G) (the smallest k for which
conflict-free k-colorings exist). We provide results both for closed
neighborhoods N[v], for which a vertex v is a member of its neighborhood, and
for open neighborhoods N(v), for which vertex v is not a member of its
neighborhood.
For closed neighborhoods, we prove the conflict-free variant of the famous
Hadwiger Conjecture: If an arbitrary graph G does not contain K_{k+1} as a
minor, then chi_CF(G) <= k. For planar graphs, we obtain a tight worst-case
bound: three colors are sometimes necessary and always sufficient. We also give
a complete characterization of the computational complexity of conflict-free
coloring. Deciding whether chi_CF(G)<= 1 is NP-complete for planar graphs G,
but polynomial for outerplanar graphs. Furthermore, deciding whether
chi_CF(G)<= 2 is NP-complete for planar graphs G, but always true for
outerplanar graphs. For the bicriteria problem of minimizing the number of
colored vertices subject to a given bound k on the number of colors, we give a
full algorithmic characterization in terms of complexity and approximation for
outerplanar and planar graphs.
For open neighborhoods, we show that every planar bipartite graph has a
conflict-free coloring with at most four colors; on the other hand, we prove
that for k in {1,2,3}, it is NP-complete to decide whether a planar bipartite
graph has a conflict-free k-coloring. Moreover, we establish that any general}
planar graph has a conflict-free coloring with at most eight colors.Comment: 30 pages, 17 figures; full version (to appear in SIAM Journal on
Discrete Mathematics) of extended abstract that appears in Proceeedings of
the Twenty-Eighth Annual ACM-SIAM Symposium on Discrete Algorithms (SODA
2017), pp. 1951-196
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