Results 141 to 150 of about 238 (165)

Exact Algorithms for Graph Homomorphisms

Theory of Computing Systems, 2005
Graph homomorphism, also called H-coloring, is a natural generalization of graph coloring: There is a homomorphism from a graph G to a complete graph on k vertices if and only if G is k-colorable. During recent years the topic of exact (exponential-time) algorithms for NP-hard problems in general, and for graph coloring in particular, has led to ...
Fedor V. Fomin, Pinar Heggernes, Dieter Kratsch   +2 more
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The Homomorphism Structure of Classes of Graphs

Combinatorics, Probability and Computing, 1999
We consider three aspects of homomorphisms of graphs and hypergraphs which are related to the structure of colour classes: (1) density, (2) the fractal property and (3) the generation of colour classes. In particular, we prove a density theorem for hypergraphs and show that, for connected oriented graphs, all jumps are balanced (and give an example ...
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Graphs and Homomorphisms

2016
Aside from ordered sets, the fixed point property has been investigated in other settings. On one hand, the fixed point property is most likely originated in topology. (See Exercise 6-1 for the topological fixed point property.) On the other hand, in any branch of mathematics in which the underlying structures have a natural type of morphism, we can ...
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Homomorphisms of graphs into odd cycles

Journal of Graph Theory, 1988
AbstractWe give a class of graphs G for which there exists a homomorphism (= adjacency preserving map) from V(G) to V(C), where C is the shortest odd cycle in G, thereby extending a result of Albertson, Catlin, and Gibbons. Our class of graphs is characterized by the following property: For each odd subdivision G′ of G there exists a homomorphic map ...
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The partial order of graphs and homomorphisms

2004
Abstract This chapter considers the partial order on graphs induced by the existence of homomorphisms. This order is rich enough to represent all countable partial orders. It discusses antichains in the homomorphism order, i.e., collections of incomparable graphs (graphs without homomorphisms between any two of them).
Pavol Hell, Jaroslav Nešetřil
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Graph homomorphisms

2021
Pavol Hell, Jaroslav Nešetřil
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Counting Homomorphisms to $K_4$-Minor-Free Graphs, Modulo 2

SIAM Journal on Discrete Mathematics, 2021
Stanislav Zivny, Jacob Focke, Leslie Goldberg   +2 more
exaly  

On counting homomorphisms to directed acyclic graphs

Journal of the ACM, 2007
Martin Dyer, Leslie Goldberg, Goldbergleslie Ann   +2 more
exaly  

On recognizing graphs by numbers of homomorphisms

Journal of Graph Theory, 2010
Zdenek Dvorak
exaly  

Homomorphisms from sparse graphs with large girth

Journal of Combinatorial Theory Series B, 2004
O V Borodin, A V Kostochka
exaly