Regularization and approximation of linear operator equations in reproducing kernel spaces
M. Zuhair Nashed, Grace Wahba · Bulletin of the American Mathematical Society · 1974
linear operator with domain V(A) C X and range in Y. An element u G V(A) is said to be a least-squares solution of the equation (1) Ax=y for a given y G Y if inf {\\\\Ax- y I: x G V(A)} = \\\\Au- y II. A pseudosolution