Abstract
In this article, we study the problem of deciding if, for a fixed graph H, a given graph is switching equivalent to an H-free graph. Polynomial-time algorithms are known for H having at most three vertices or isomorphic to P-4.
We show that for H isomorphic to a claw, the problem is polynomial, too. On the other hand, we give infinitely many graphs H such that the problem is NP-complete, thus solving an open problem [Kratochvil, Neetil and Zyka, Ann Discrete Math 51 (1992)].
Further, we give a characterization of graphs switching equivalent to a K-1,K- 2-free graph by ten forbidden-induced subgraphs, each having five vertices. We also give the forbidden-induced subgraphs for graphs switching equivalent to a forest of bounded vertex degrees.