Module « numpy.random »

Fonction wald - module numpy.random

Signature de la fonction wald

Description

wald.__doc__

        wald(mean, scale, size=None)

        Draw samples from a Wald, or inverse Gaussian, distribution.

        As the scale approaches infinity, the distribution becomes more like a
        Gaussian. Some references claim that the Wald is an inverse Gaussian
        with mean equal to 1, but this is by no means universal.

        The inverse Gaussian distribution was first studied in relationship to
        Brownian motion. In 1956 M.C.K. Tweedie used the name inverse Gaussian
        because there is an inverse relationship between the time to cover a
        unit distance and distance covered in unit time.

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

        Parameters
        ----------
        mean : float or array_like of floats
            Distribution mean, must be > 0.
        scale : float or array_like of floats
            Scale parameter, 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 ``mean`` and ``scale`` are both scalars.
            Otherwise, ``np.broadcast(mean, scale).size`` samples are drawn.

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

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

        Notes
        -----
        The probability density function for the Wald distribution is

        .. math:: P(x;mean,scale) = \sqrt{\frac{scale}{2\pi x^3}}e^
                                    \frac{-scale(x-mean)^2}{2\cdotp mean^2x}

        As noted above the inverse Gaussian distribution first arise
        from attempts to model Brownian motion. It is also a
        competitor to the Weibull for use in reliability modeling and
        modeling stock returns and interest rate processes.

        References
        ----------
        .. [1] Brighton Webs Ltd., Wald Distribution,
               https://web.archive.org/web/20090423014010/http://www.brighton-webs.co.uk:80/distributions/wald.asp
        .. [2] Chhikara, Raj S., and Folks, J. Leroy, "The Inverse Gaussian
               Distribution: Theory : Methodology, and Applications", CRC Press,
               1988.
        .. [3] Wikipedia, "Inverse Gaussian distribution"
               https://en.wikipedia.org/wiki/Inverse_Gaussian_distribution

        Examples
        --------
        Draw values from the distribution and plot the histogram:

        >>> import matplotlib.pyplot as plt
        >>> h = plt.hist(np.random.wald(3, 2, 100000), bins=200, density=True)
        >>> plt.show()