NP-Completeness of Induced Matching Problem and Co-NP-Completeness of Induced Matching Extendable Problem

A matching M of a graph G is induced, if M is an induced subgraph of G. A graph G is induced matching extendable (simply IM-extendable), if every induced matching M of G is included in a perfect matching of G. In this paper we will prove the following results. (1) The problem "given a graph G and a positive integer r, determine whether there is an induced matching M of G such that |M|≥r" is NP-complete for claw-free graphs. (2) The problem "determine whether a given graph is IM-extendable" is co-NP- complete for graphs with diameter 2 and bipartite graphs with diameter 3 but linearly solvable for complete multi-partite graphs.