  To get the same results one must use the following parametrization:
    ``stats.f(dfn, dfd).cdf(x)=fdtr(dfn, dfd, x)``.

    >>> from scipy.stats import f
    >>> dfn, dfd = 1, 2
    >>> x = 1
    >>> fdtr_res = fdtr(dfn, dfd, x)  # this will often be faster than below
    >>> f_dist_res = f(dfn, dfd).cdf(x)
    >>> fdtr_res == f_dist_res  # test that results are equal
    True
    