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For a class C of graphs, #Sub(C) is the counting problem that, given a graph H from C and an arbitrary graph G, asks for the number of subgraphs of G isomorphic to H. It is known that if C has bounded vertex-cover number (equivalently, the size of the maximum matching in C is bounded), then #Sub(C) is polynomial-time solvable. We complement this result with… (More)

We prove #W[1]-hardness of the following parameterized counting problem: Given a simple undirected graph G and a parameter k ∈ N, compute the number of matchings of size k in G. It is known from [1] that, given an edge-weighted graph G, computing a particular weighted sum over the matchings in G is #W[1]-hard. In the present paper, we exhibit a reduction… (More)

We devise a framework for proving tight lower bounds under the counting exponential-time hypothesis #ETH introduced by Dell et al. (ACM Transactions on Algorithms, 2014). Our framework allows to convert many known #P-hardness results for counting problems into tight lower bounds of the following type: Assuming #ETH, the given problem admits no algorithm… (More)

- Radu Curticapean
- 2015

We identify and study relevant structural parameters for the problem PerfMatch of counting perfect matchings in a given input graph C. These generalize the well-known tractable planar case, and they include the genus of C, its apex number (the minimum number of vertices whose removal renders C planar), and its Hadwiger number (the size of a largest clique… (More)

Let P be a set of $n$ points in the plane. A crossing-free structure on P is a straight-edge planar graph with vertex set in P. Examples of crossing-free structures include triangulations of P, and spanning cycles of P, also known as polygonalizations of P, among others. There has been a large amount of research trying to bound the number of such… (More)

Given an edge-weighted graph G, let PerfMatch(G) be the following weighted sum that ranges over all perfect matchings M in G: PerfMatch(G) := M e∈M w(e). If G is unweighted, this plainly counts the perfect matchings of G. In this paper, we introduce parity separation, a new method for reducing PerfMatch to unweighted instances: For graphs G with… (More)

Let P be a set of n points in the plane. A crossing-free structure on P is a plane graph with vertex set P. Examples of crossing-free structures include trian-gulations of P , spanning cycles of P , also known as polygonalizations of P , among others. There has been a large amount of research trying to bound the number of such structures. In particular,… (More)