Two New 1-rotational \((36,9,8)\) and \((40,10,9)\) RBIBDs

We formulate the construction of 1-rotational difference families as a combinatorial optimization problem. A tabu search algorithm is used to find an optimal solution to the optimization problem for various 1-rotational difference family parameters. In particular, we construct two new 1-rotational difference families which lead to an equal number of new 1-rotational RBIBDs with parameters: \((36, 9, 8)\) and \((40, 10, 9)\). Our algorithm also was able to construct six non-isomorphic \((36, 9, 8)\) and three \((40, 10, 9)\) RBIBDs