It is known that for a nonsingular matrix A and two vectors and w, the matrix (A+) is nonsingular iff A-1 and then (A + uw) = A A ¹uw A 1 1+WTA ¹u How to use this fact to solve the following problem. We are given a QR = A decomposition of A and we want to solve B = b. The matrix B is nonsingular matrix and differs from for ikor j 1. (What are the == A in only one entry, say bk,l=c+ak,l and bij corresponding vectors u and w?) == aij