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The mathematical and numerical least squares solution of a general linear system of equations is discussed.Perturbation and differentiability theorems for pseudoinverses are given.Computational procedures for calculating least squares solutions using orthonormal transformations, multiplying matrices by a matrix of orthonormal basis vectors for the null-space of a given matrix, sequential processing of data, and processing of block diagonal matrices form a partial list of numerical topics presented.
Hanson et al. (Wed,) studied this question.