On the amicability of orthogonal designs

Although it is known that the maximum number of variables in two amicable orthogonal designs of order 2 n p , where p is an odd integer, never exceeds 2 n +2, not much is known about the existence of amicable orthogonal designs lacking zero entries that have 2 n +2 variables in total. In this paper we develop two methods to construct amicable orthogonal designs of order 2 n p where p odd, with no zero entries and with the total number of variables equal or nearly equal to 2 n +2. In doing so, we make a surprising connection between the two concepts of amicable sets of matrices and an amicable pair of matrices. With the recent discovery of a link between the theory of amicable orthogonal designs and space‐time codes, this paper may have applications in space‐time codes. © 2009 Wiley Periodicals, Inc. J Combin Designs 17: 240‐252, 2009