.  If you ever find yourself multiplying by the inverse, then you
% know one thing for sure.  You know with certainty that you don't know
% what you're doing.

A = rand (500) ;
tic ; S1 = inv (A) ;            ; toc
tic ; S2 = double (inverse (A)) ; toc
norm (S1-S2)

A = rand (500,400) ;
tic ; S1 = pinv (A)             ; toc
tic ; S2 = double (inverse (A)) ; toc
norm (S1-S2)

%% Update/downdate of a dense Cholesky factorization
%
% Wilkinson considered the update/downdate of a matrix factorization to be
% a 