dy = (x[i][1] + ybox*yprd) - xcm[1];

      dz = (x[i][2] + zbox*zprd) - xcm[2];

      v[i][0] -= omega[1]*dz - omega[2]*dy;

      v[i][1] -= omega[2]*dx - omega[0]*dy;

      v[i][1] -= omega[2]*dx - omega[0]*dz;

      v[i][2] -= omega[0]*dy - omega[1]*dx;

    }

}