  A k-regular graph on v vertices is a divisible design graph with parameters
(v, k, lambda_1 ,lambda_2, m, n) if its vertex set can be partitioned into m
classes of size n, such that any two different vertices from the same class
have lambda_1 common neighbours, and any two vertices from different classes
have lambda_2 common neighbours whenever it is not complete or edgeless. If
m=1, then a divisible design graph is strongly regular with parameters (v, k,
lambda_1, lambda_1). In this paper the Wallis-Fon-Der-Flaass construction of
strongly regular graphs is modified to create new constructions of divisible
design graphs. In some cases, these constructions lead to strongly regular
graphs.

Combinatorics