to `bdtr` with respect to `p`.

    Finds the event probability `p` such that the sum of the terms 0 through
    `k` of the binomial probability density is equal to the given cumulative
    probability `y`.

    Parameters
    ----------
    k : array_like
        Number of successes (float), rounded down to the nearest integer.
    n : array_like
        Number of events (float)
    y : array_like
        Cumulative probability (probability of `k` or fewer successes in `n`
        events).
    out : ndarray, optional
        Optional output array for the function values

    Returns
    -------
    p : scalar or ndarray
        The event probability such that `bdtr(\lfloor k \rfloor, n, p) = y`.

    See Also
    --------
    bdtr
    betaincinv

    Notes
    -----
    The computation is carried out using the inverse beta integral function
    and the relation,::

        1 - p = betaincinv(n - k, k + 1, y).

    Wrapper for the Cephes [1]_ routine `bdtri`.

    References
    ----------
    .. [1] Cephes Mathematical Functions Library,
           http://www.netlib.org/cephes/
    