      ; toc
tic ; S2 = double (inverse (A)) ; toc
norm (S1-S2)
</pre><pre class="codeoutput">Elapsed time is 0.108800 seconds.
Elapsed time is 0.147705 seconds.
ans =
   3.1817e-11
Elapsed time is 1.680637 seconds.
Elapsed time is 0.193965 seconds.
ans =
   3.8189e-14
</pre><h2>Update/downdate of a dense Cholesky factorization<a name="18"></a></h2>
         <p>Wilkinson considered the update/downdate of a matrix factorization to be a key problem in computational linear algebra.  The
            idea is that