oc, norm (A'*A*x-A'*b)
tic ; x = factorize(A)\b ; toc, norm (A'*A*x-A'*b)

%%
% FACTORIZE is better than BACKSLASH because you can reuse the
% factorization for different right-hand-sides.  For full-rank matrices,
% it's better than PINV because it's faster (and PINV fails for sparse
% matrices).

A = rand (1000,200) ;
b = rand (1000,1) ;
c = rand (1000,1) ;

tic ;                  ; x = A\b ; y = A\c ; toc
tic ; S = pinv(A)      ; x = S*b ; y = S*c ; toc
tic ; S = inverse(A)   ; x = S*b ; y = S*c ; toc
tic