Induced forests in some distance-regular graphs

In this article, we study the order and structure of the largest induced forests in some families of graphs. First we prove a variation of the Delsarte-Hoffman ratio bound for cocliques that gives an upper bound on the order of the largest induced forest in a graph. Next we define a canonical induced forest to be a forest that is formed by adding a vertex to a coclique and give several examples of graphs where the maximal forest is a canonical induced forest. These examples are all distance-regular graphs with the property that the Delsarte-Hoffman ratio bound for cocliques holds with equality. We conclude with some examples of related graphs where there are induced forests that are larger than a canonical forest. (c) 2023 Elsevier B.V. All rights reserved.