  A complex Hadamard matrix is a square matrix W with complex entries of
absolute value 1 satisfying WW*=nI, where * stands for the Hermitian transpose
and I is the identity matrix of order n. In this paper, we give constructions
of complex Hadamard matrices in the Bose-Mesner algebra of a certain 4-class
symmetric association scheme. Moreover, we determine the Nomura algebras to
show that the resulting matrices are not decomposable into nontrivial
generalized tensor products.
