Completely Independent Spanning Trees in (Partial) k-Trees

Abstract Two spanning trees T1 and T2 of a graph G are completely independent if, for any two vertices u and v, the paths from u to v in T1 and T2 are internally disjoint. For a graph G, we denote the maximum number of pairwise completely independent spanning trees by cist(G). In this paper, we consider cist(G) when G is a partial k-tree. First we show that [k/2] ≤ cist(G) ≤ k − 1 for any k-tree G. Then we show that for any p ∈ {[k/2], . . . , k − 1}, there exist infinitely many k-trees G such that cist(G) = p. Finally we consider algorithmic aspects for computing cist(G). Using Courcelle’s theorem, we show that there is a linear-time algorithm that computes cist(G) for a partial k-tree, where k is a fixed constant.