Counting homomorphisms in plain exponential time
Data Structures and Algorithms
2018-10-09 v1 Computational Complexity
Combinatorics
Abstract
In the counting Graph Homomorphism problem (#GraphHom) the question is: Given graphs G,H, find the number of homomorphisms from G to H. This problem is generally #P-complete, moreover, Cygan et al. proved that unless the ETH is false there is no algorithm that solves this problem in time O(|V(H)|^{o(|V(G)|)}. This, however, does not rule out the possibility that faster algorithms exist for restricted problems of this kind. Wahlstrom proved that #GraphHom can be solved in plain exponential time, that is, in time k^{|V(G)|+V(H)|}\poly(|V(H)|,|V(G)|) provided H has clique width k. We generalize this result to a larger class of graphs, and also identify several other graph classes that admit a plain exponential algorithm for #GraphHom.
Cite
@article{arxiv.1810.03087,
title = {Counting homomorphisms in plain exponential time},
author = {Amineh Dadsetan and Andrei A. Bulatov},
journal= {arXiv preprint arXiv:1810.03087},
year = {2018}
}