Module « numpy.random »

Fonction noncentral_f - module numpy.random

Signature de la fonction noncentral_f

Description

noncentral_f.__doc__

        noncentral_f(dfnum, dfden, nonc, size=None)

        Draw samples from the noncentral F distribution.

        Samples are drawn from an F distribution with specified parameters,
        `dfnum` (degrees of freedom in numerator) and `dfden` (degrees of
        freedom in denominator), where both parameters > 1.
        `nonc` is the non-centrality parameter.

        .. note::
            New code should use the ``noncentral_f`` method of a ``default_rng()``
            instance instead; please see the :ref:`random-quick-start`.

        Parameters
        ----------
        dfnum : float or array_like of floats
            Numerator degrees of freedom, must be > 0.

            .. versionchanged:: 1.14.0
               Earlier NumPy versions required dfnum > 1.
        dfden : float or array_like of floats
            Denominator degrees of freedom, must be > 0.
        nonc : float or array_like of floats
            Non-centrality parameter, the sum of the squares of the numerator
            means, must be >= 0.
        size : int or tuple of ints, optional
            Output shape.  If the given shape is, e.g., ``(m, n, k)``, then
            ``m * n * k`` samples are drawn.  If size is ``None`` (default),
            a single value is returned if ``dfnum``, ``dfden``, and ``nonc``
            are all scalars.  Otherwise, ``np.broadcast(dfnum, dfden, nonc).size``
            samples are drawn.

        Returns
        -------
        out : ndarray or scalar
            Drawn samples from the parameterized noncentral Fisher distribution.

        See Also
        --------
        Generator.noncentral_f: which should be used for new code.

        Notes
        -----
        When calculating the power of an experiment (power = probability of
        rejecting the null hypothesis when a specific alternative is true) the
        non-central F statistic becomes important.  When the null hypothesis is
        true, the F statistic follows a central F distribution. When the null
        hypothesis is not true, then it follows a non-central F statistic.

        References
        ----------
        .. [1] Weisstein, Eric W. "Noncentral F-Distribution."
               From MathWorld--A Wolfram Web Resource.
               http://mathworld.wolfram.com/NoncentralF-Distribution.html
        .. [2] Wikipedia, "Noncentral F-distribution",
               https://en.wikipedia.org/wiki/Noncentral_F-distribution

        Examples
        --------
        In a study, testing for a specific alternative to the null hypothesis
        requires use of the Noncentral F distribution. We need to calculate the
        area in the tail of the distribution that exceeds the value of the F
        distribution for the null hypothesis.  We'll plot the two probability
        distributions for comparison.

        >>> dfnum = 3 # between group deg of freedom
        >>> dfden = 20 # within groups degrees of freedom
        >>> nonc = 3.0
        >>> nc_vals = np.random.noncentral_f(dfnum, dfden, nonc, 1000000)
        >>> NF = np.histogram(nc_vals, bins=50, density=True)
        >>> c_vals = np.random.f(dfnum, dfden, 1000000)
        >>> F = np.histogram(c_vals, bins=50, density=True)
        >>> import matplotlib.pyplot as plt
        >>> plt.plot(F[1][1:], F[0])
        >>> plt.plot(NF[1][1:], NF[0])
        >>> plt.show()