>>> from scipy.special import fdtridfd, fdtr
    >>> dfn, dfd, x = 10, 5, 2
    >>> cdf_value = fdtr(dfn, dfd, x)
    >>> cdf_value
    0.7700248806501017

    Verify that `fdtridfd` recovers the original value for `dfd`:

    >>> fdtridfd(dfn, cdf_value, x)
    5.0
    Ú