A Latin square of order s is an s by s array L of the symbols { 1,2,..., s}, such that each symbol occurs once in each row and column of L. Two Latin squares L and M of order s are orthogonal if their superposition yields all s2 possible ordered pairs (i,j), 1 < i, j < s. It was conjectured by Euler, and proved by Tarry [4] that there do not exist a pair of orthogonal Latin squares of order six...

A Howell design of side s and order 2n, or more briefly an H(s, 2n), is an s x s array in which each cell is either empty or contains an unordered pair of elements from some (2n)-set V such that (1) every element of V occurs in precisely one cell of each row and each column, and (2) every unordered pair of elements from V is in at most one cell of the array. It follows immediately from the defi...

Abstract. In an earlier paper the authors constructed a hamilton cycle embedding of Kn,n,n in a nonorientable surface for all n ≥ 1 and then used these embeddings to determine the genus of some large families of graphs. In this two-part series, we extend those results to orientable surfaces for all n 6= 2. In part I, we explore a connection between orthogonal latin squares and embeddings. A pro...

We explore classical (relative) difference sets intersected with the cosets of a subgroup of small index. The intersection sizes are governed by quadratic Diophantine equations. Developing the intersections in the subgroup yields an interesting class of group divisible designs. From this and the Bose-Shrikhande-Parker construction, we obtain some new sets of mutually orthogonal latin squares. W...

We prove that complete sets of orthogonal diagonal Sudoku latin squares (sometimes called Sudoku frames) exist of all orders p, where p is a prime. We also show that complete sets of orthogonal Sudoku frames which are left semi-diagonal exist of all orders p, s > 1. We conjecture that these may be right semi-diagonal also but we do not have a general proof. We show how these complete sets may b...

To study orthogonal arrays and signed orthogonal arrays, Ray-Chaudhuri and Singhi (1988 and 1994) considered some module spaces. Here, using a linear algebraic approach we define an inclusion matrix and find its rank. In the special case of Latin squares we show that there is a straightforward algorithm for generating a basis for this matrix using the so-called intercalates. We also extend this...