Sankhyā: The Indian Journal of Statistics, Series A (1961-2002), Vol. 38, No. 4 (Oct., 1976), pp. 400-403 (4 pages) A theorem involving the decomposition of an idempotent matrix into the sum of one or ...

A flexible method is introduced to model the structure of a covariance matrix C and study the dependence of the covariances on explanatory variables by observing that for any real symmetric matrix A, ...