Approximately Counting H-Colorings is #BIS-Hard
Andreas Galanis
Department of Computer Science, University of Oxford, Oxford, UK
Department of Computer Science, University of Oxford, Oxford, UK
2015/7/13 Mon 11AM-12PM
We consider the problem of counting H-colorings from an input graph G to a target graph H. (An H-coloring of G is a homomorphism from the graph G to the graph H.)
We show that if H is any fixed graph without trivial components, then the problem is as hard as the well-known problem #BIS, which is the problem of (approximately) counting independent sets in a bipartite graph. #BIS is a complete problem in a important complexity class for approximate counting, and is widely believed not to have an FPRAS. If this is so, then our result shows that for every graph H without trivial components, the H-coloring counting problem has no FPRAS.
This problem was studied a decade ago by Goldberg, Kelk and Paterson. They were able to show that approximately sampling H-colorings is #BIS-hard, but it was not known how to get the result for approximate counting. Our solution builds on non-constructive ideas using the work of Lovasz.
Joint work with Leslie Goldberg and Mark Jerrum.
We show that if H is any fixed graph without trivial components, then the problem is as hard as the well-known problem #BIS, which is the problem of (approximately) counting independent sets in a bipartite graph. #BIS is a complete problem in a important complexity class for approximate counting, and is widely believed not to have an FPRAS. If this is so, then our result shows that for every graph H without trivial components, the H-coloring counting problem has no FPRAS.
This problem was studied a decade ago by Goldberg, Kelk and Paterson. They were able to show that approximately sampling H-colorings is #BIS-hard, but it was not known how to get the result for approximate counting. Our solution builds on non-constructive ideas using the work of Lovasz.
Joint work with Leslie Goldberg and Mark Jerrum.