def vectorial_product(u, v):
    """
    Vectorial product u x v. Vectors u, v should be tuple of
    floats or tuple of arrays, (ux, uy, uz) and (vx, vy, vz)
    """
    return (u[1]*v[2] - u[2]*v[1],
            u[2]*v[0] - u[0]*v[2],
            u[0]*v[1] - u[1]*v[0])