Abstract
A simple connected graph G with 2n vertices is said to be k-extendable for an integer k with \(0<k<n\) if G contains a perfect matching and every matching of cardinality k in G is a subset of some perfect matching. Lakhal and Litzler (Inf Process Lett 65(1):11–16, 1998) discovered a polynomial algorithm that decides whether a bipartite graph is k-extendable. For general graphs, however, it has been an open problem whether there exists a polynomial algorithm. The new result presented in this paper is that the extendability problem is co-NP-complete.
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Hackfeld, J., Koster, A.M.C.A. The matching extension problem in general graphs is co-NP-complete. J Comb Optim 35, 853–859 (2018). https://doi.org/10.1007/s10878-017-0226-x
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DOI: https://doi.org/10.1007/s10878-017-0226-x