On computing an optimal semi-matching

  • Authors:
  • Franti$#353/ek Galč/í/k;J$#225/n Katrenič/;Gabriel Semani$#353/in

  • Affiliations:
  • Institute of Computer Science, P.J. Š/af$#225/rik University, Faculty of Science, Ko$#353/ice, Slovak Republic;Institute of Computer Science, P.J. Š/af$#225/rik University, Faculty of Science, Ko$#353/ice, Slovak Republic;Institute of Computer Science, P.J. Š/af$#225/rik University, Faculty of Science, Ko$#353/ice, Slovak Republic

  • Venue:
  • WG'11 Proceedings of the 37th international conference on Graph-Theoretic Concepts in Computer Science
  • Year:
  • 2011

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Abstract

The problem of finding an optimal semi-matching is a generalization of the problem of finding classical matching in bipartite graphs. A semi-matching in a bipartite graph G=(U, V, E) with n vertices and m edges is a set of edges M⊆E, such that each vertex in U is incident to at most one edge in M. An optimal semi-matching is a semi-matching with degM(u)=1 for all u∈U and the minimal value of $\sum_{v \in V} \frac{deg_M(v).(deg_M(v)+1)}2$ . We propose a schema that allows a reduction of the studied problem to a variant of the maximum bounded-degree semi-matching problem. The proposed schema yields to two algorithms for computing an optimal semi-matching. The first one runs in time $O(\sqrt{n} \cdot m \cdot \log{n})$ that is the same as the time complexity of the currently best known algorithm. However, our algorithm uses a different approach that enables some improvements in practice (e.g. parallelization, faster algorithms for special graph classes). The second one is randomized and it computes an optimal semi-matching with high probability in O(nω ·log1+o(1)n), where ω is the exponent of the best known matrix multiplication algorithm. Since ω≤2.38, this algorithms breaks through O(n2.5) barrier for dense graphs.