kl\_div}(x, y) =
          \begin{cases}
            x \log(x / y) - x + y & x > 0, y > 0 \\
            y & x = 0, y \ge 0 \\
            \infty & \text{otherwise}
          \end{cases}

    Parameters
    ----------
    x, y : array_like
        Real arguments
    out : ndarray, optional
        Optional output array for the function results

    Returns
    -------
    scalar or ndarray
        Values of the Kullback-Liebler divergence.

    See Also
    --------
    entr, rel_entr, scipy.stats.entropy

    Notes
    -----
    .. versionadded:: 0.15.0

    This function is non-negative and is jointly convex in `x` and `y`.

    The origin of this function is in convex programming; see [1]_ for
    details. This is why the function contains the extra :math:`-x
    + y` terms over what might be expected from the Kullback-Leibler
    divergence. For a version of the function without the extra terms,
    see `rel_entr`.

    References
    ----------
    .. [1] Boyd, Stephen and Lieven Vandenberghe. *Convex optimization*.
           Cambridge University Press, 2004.
           :doi:`https://doi.org/10.1017/CBO9780511804441`

    Ú