def scott_rule_of_thumb(n_samples, dimension):
    """
    Scott's rule of thumb.

    .. math::

       \\left ( \\frac{1}{n} \\right ) ^{\\frac{1}{d+4}}

    (see also scipy.stats.kde.gaussian_kde.scotts_factor)
    """
    return n_samples ** (-1. / (dimension + 4))