Combinatorial structure of group divisible designs without α-resolution classes in each group Original Research Article

It is known that group divisible designs (GDDs) with r=λ1+1 are regular and symmetric, and that the combinatorial structure of these designs is characterized in terms of Hadamard tournaments and strongly regular graphs. In this paper, it is shown that GDDs without α-resolution classes in each group are also specified by Hadamard tournaments and strongly regular graphs. The result given by Jimbo and Kageyama (ICA Bull. 32 (2001) 29) is included in the present result as a special case.