def quaternion_conjugate(q):
    """Conjugate of a quaternion.

    Parameters
    ----------
    q : list
        Quaternion as a list of four real values ``[w, x, y, z]``.

    Returns
    -------
    list
        Conjugate quaternion as a list of four real values ``[cw, cx, cy, cz]``.

    References
    ----------
    .. _mathworld quaternion conjugate: http://mathworld.wolfram.com/QuaternionConjugate.html
    """
    return [q[0], -q[1], -q[2], -q[3]]