Approximation algorithm for the multicovering problem

Abstract

Let \(\mathcal {H}=(V,\mathcal {E})\) be a hypergraph with maximum edge size \(\ell \) and maximum degree \(\varDelta \). For a given positive integers \(b_v\), \(v\in V\), a set multicover in \(\mathcal {H}\) is a set of edges \(C \subseteq \mathcal {E}\) such that every vertex v in V belongs to at least \(b_v\) edges in C. Set multicover is the problem of finding a minimum-cardinality set multicover. Peleg, Schechtman and Wool conjectured that for any fixed \(\varDelta \) and \(b:=\min _{v\in V}b_{v}\), the problem of set multicover is not approximable within a ratio less than \(\delta :=\varDelta -b+1\), unless \(\mathcal {P}=\mathcal {NP}\). Hence it’s a challenge to explore for which classes of hypergraph the conjecture doesn’t hold. We present a polynomial time algorithm for the set multicover problem which combines a deterministic threshold algorithm with conditioned randomized rounding steps. Our algorithm yields an approximation ratio of \(\max \left\{ \frac{148}{149}\delta , \left( 1- \frac{ (b-1)e^{\frac{\delta }{4}}}{94\ell } \right) \delta \right\} \) for \(b\ge 2\) and \(\delta \ge 3\). Our result not only improves over the approximation ratio presented by El Ouali et al. (Algorithmica 74:574, 2016) but it’s more general since we set no restriction on the parameter \(\ell \). Moreover we present a further polynomial time algorithm with an approximation ratio of \(\frac{5}{6}\delta \) for hypergraphs with \(\ell \le (1+\epsilon )\bar{\ell }\) for any fixed \(\epsilon \in [0,\frac{1}{2}]\), where \(\bar{\ell }\) is the average edge size. The analysis of this algorithm relies on matching/covering duality due to Ray-Chaudhuri (1960), which we convert into an approximative form. The second performance disprove the conjecture of Peleg et al. for a large subclass of hypergraphs.