Clique graphs of chordal and path graphs

Abstract

We characterize clique graphs of chordal and path graphs. A special class of graphs called expanded trees is introduced. They form a subclass of disk-Helly graphs. It is shown that the clique graph of every chordal (hence path) graph is an expanded tree. In addition, every expanded tree is the clique graph of some path (hence chordal) graph. Different characterizations of expanded trees are described, leading to a polynomial time algorithm for recognizing clique graphs of chordal and path graphs.