GMRES   Generalized Minimum Residual Method.
 
    X = gmres(A,B) attempts to solve the square linear system A*X=B via
    the GMRES method.
 
    This routine is simply a wrapper to Matlab's own GMRES routine,
    and the argument list variations described in Matlab's GMRES
    documentation are also allowed here.  The usage is identical to
    Matlab's default version, except that the first argument must be a
    Spot operator.