Some algorithms based upon a projection process onto the Krylov subspace $K_m = \operatorname{Span}(r_0, Ar_0, \ldots, A^{m - 1}r_0)$ are developed, generalizing the ...
Mathematics of Computation, Vol. 23, No. 108 (Oct., 1969), pp. 787-812 (26 pages) The mathematical and numerical least squares solution of a general linear system of equations is discussed.