Comparing Universal Covers in Polynomial Time

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Comparing Universal Covers in Polynomial Time
The universal cover TG of a connected graph G is the unique (possible infinite) tree covering G, i.e., that allows a locally bijective homomorphism from TG to G. Universal covers have major applications in the area of distributed computing. It is well-known that if a graph G covers a graph H then their universal covers are isomorphic, and that the latter can be tested in polynomial time by checking if G and H share the same degree refinement matrix. We extend this result to locally injective and locally surjective homomorphisms by following a very different approach. Using linear programming techniques we design two polynomial time algorithms that check if there exists a locally injective or a locally surjective homomorphism, respectively, from a universal cover TG to a universal cover TH . This way we obtain two heuristics for testing the corresponding locally constrained graph homomorphisms. As a consequence, we have obtained a new polynomial time algorithm for testing (subgraph) iso...
Jirí Fiala, Daniël Paulusma
Added 19 Oct 2010
Updated 19 Oct 2010
Type Conference
Year 2008
Where CSR
Authors Jirí Fiala, Daniël Paulusma
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