   toc ;
tic ; S3 = A - (B/D)*C ;    toc ;

%% So the winner is ... nobody
%
% BACKSLASH: mostly simple to use (except remember that Schur complement
%       formula?).  Fast and accurate ... but slow if you want to solve
%       two linear systems with the same matrix A.
%
% LU, QR, CHOL: fast and accurate.  Awful syntax to use.  Drag out your
%       linear algebra textbook if you want to use these in MATLAB.
%       Whenever I use them I have to derive them from scratch, even
%       though I *wrote* mos