Finding vertex-surjective graph homomorphisms
نویسندگان
چکیده
منابع مشابه
On the extension of vertex maps to graph homomorphisms
A reflexive graph is a simple undirected graph where a loop has been added at each vertex. If G and H are reflexive graphs and U ⊆ V (H), then a vertex map f : U → V (G) is called nonexpansive if for every two vertices x, y ∈ U , the distance between f(x) and f(y) in G is at most that between x and y in H . A reflexive graph G is said to have the extension property (EP) if for every reflexive g...
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Focke, Goldberg, and Živný [4] prove a complexity dichotomy for the problem of counting surjective homomorphisms from a large input graph G without loops to a fixed graph H that may have loops. In this note, we give a short proof of a weaker result: Namely, we only prove the #P-hardness of the more general problem in which G may have loops. Our proof is an application of a powerful framework of...
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A homomorphism from a graph G to a graph H is a function from the vertices of G to the vertices of H that preserves edges. A homomorphism is surjective if it uses all of the vertices of H and it is a compaction if it uses all of the vertices of H and all of the non-loop edges of H . Hell and Nešetřil gave a complete characterisation of the complexity of deciding whether there is a homomorphism ...
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ژورنال
عنوان ژورنال: Acta Informatica
سال: 2012
ISSN: 0001-5903,1432-0525
DOI: 10.1007/s00236-012-0164-0