you can't use 'Q' if the
% matrix is full.  But LINSOLVE doesn't work on sparse matrices.
%
% But ... Ack!  That's getting complicated ...
%
% Here's the best way to solve A*x=b and A*y=c when A is full and
% unsymmetric:

n = 1000 ;
A = rand (n) ;
b = rand (n,1) ;
c = rand (n,1) ;
tic ; [L,U,p] = lu (A, 'vector') ; LUtime = toc

tic ; x = U \ (L \ b (p,:)) ;
      y = U \ (L \ c (p,:)) ; toc

tic ; opL = struct ('LT', true) ;
      opU = struct ('UT', true) ;
      x = linsolve (U, linsolve (L, b(p,:), opL