Title: A generalization of the Eckart-Young-Mirsky matrix approximation theorem
Abstract: The Eckart-Young-Mirsky theorem solves the problem of approximating a matrix by one of lower rank. However, the approximation generally differs from the original in all its elements. In this paper it is shown how to obtain a best approximation of lower rank in which a specified set of columns of the matrix remains fixed. The paper concludes with some applications of the generalization.