def trail_vector_out(tvec_in, q_vec, rd_vec, ri_vec):
    """
    Calculate an outgoing trail vector.

    Parameters
    ----------
    tvec_in : ``list``
        An incoming trail vector.
    q_vec : ``list``
        A load vector.
    rd_vec : ``list``
        The direct deviation edges resultant force vector.
    ri_vec : ``list``
        The indirect deviation edges resultant force vector.

    Returns
    -------
    tvec_out : ``list``
        An outgoing trail vector.
    """
    return -1.0 * (tvec_in + q_vec + rd_vec + ri_vec)