const ColumnVector	openx	= args(8).VECTOR_VALUE();
#endif // STANDALONE

  static DAEFunc fdae(mtt_residual);
  static ColumnVector XX (Nx+Nyz);
  XX.insert (x,0);

  for (register int i = Nx; i < Nyz; i++)
  for (register int i = Nx; i < Nx+Nyz; i++)
    XX(i) = 0.0;

  double tout = t + ddt;

  DASSL fdassl (XX, t, fdae);
  x = fdassl.do_integrate (tout).extract (0,Nx-1);