Module « numpy.random »

Fonction gumbel - module numpy.random

Signature de la fonction gumbel

Description

gumbel.__doc__

        gumbel(loc=0.0, scale=1.0, size=None)

        Draw samples from a Gumbel distribution.

        Draw samples from a Gumbel distribution with specified location and
        scale.  For more information on the Gumbel distribution, see
        Notes and References below.

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

        Parameters
        ----------
        loc : float or array_like of floats, optional
            The location of the mode of the distribution. Default is 0.
        scale : float or array_like of floats, optional
            The scale parameter of the distribution. Default is 1. Must be non-
            negative.
        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 ``loc`` and ``scale`` are both scalars.
            Otherwise, ``np.broadcast(loc, scale).size`` samples are drawn.

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

        See Also
        --------
        scipy.stats.gumbel_l
        scipy.stats.gumbel_r
        scipy.stats.genextreme
        weibull
        Generator.gumbel: which should be used for new code.

        Notes
        -----
        The Gumbel (or Smallest Extreme Value (SEV) or the Smallest Extreme
        Value Type I) distribution is one of a class of Generalized Extreme
        Value (GEV) distributions used in modeling extreme value problems.
        The Gumbel is a special case of the Extreme Value Type I distribution
        for maximums from distributions with "exponential-like" tails.

        The probability density for the Gumbel distribution is

        .. math:: p(x) = \frac{e^{-(x - \mu)/ \beta}}{\beta} e^{ -e^{-(x - \mu)/
                  \beta}},

        where :math:`\mu` is the mode, a location parameter, and
        :math:`\beta` is the scale parameter.

        The Gumbel (named for German mathematician Emil Julius Gumbel) was used
        very early in the hydrology literature, for modeling the occurrence of
        flood events. It is also used for modeling maximum wind speed and
        rainfall rates.  It is a "fat-tailed" distribution - the probability of
        an event in the tail of the distribution is larger than if one used a
        Gaussian, hence the surprisingly frequent occurrence of 100-year
        floods. Floods were initially modeled as a Gaussian process, which
        underestimated the frequency of extreme events.

        It is one of a class of extreme value distributions, the Generalized
        Extreme Value (GEV) distributions, which also includes the Weibull and
        Frechet.

        The function has a mean of :math:`\mu + 0.57721\beta` and a variance
        of :math:`\frac{\pi^2}{6}\beta^2`.

        References
        ----------
        .. [1] Gumbel, E. J., "Statistics of Extremes,"
               New York: Columbia University Press, 1958.
        .. [2] Reiss, R.-D. and Thomas, M., "Statistical Analysis of Extreme
               Values from Insurance, Finance, Hydrology and Other Fields,"
               Basel: Birkhauser Verlag, 2001.

        Examples
        --------
        Draw samples from the distribution:

        >>> mu, beta = 0, 0.1 # location and scale
        >>> s = np.random.gumbel(mu, beta, 1000)

        Display the histogram of the samples, along with
        the probability density function:

        >>> import matplotlib.pyplot as plt
        >>> count, bins, ignored = plt.hist(s, 30, density=True)
        >>> plt.plot(bins, (1/beta)*np.exp(-(bins - mu)/beta)
        ...          * np.exp( -np.exp( -(bins - mu) /beta) ),
        ...          linewidth=2, color='r')
        >>> plt.show()

        Show how an extreme value distribution can arise from a Gaussian process
        and compare to a Gaussian:

        >>> means = []
        >>> maxima = []
        >>> for i in range(0,1000) :
        ...    a = np.random.normal(mu, beta, 1000)
        ...    means.append(a.mean())
        ...    maxima.append(a.max())
        >>> count, bins, ignored = plt.hist(maxima, 30, density=True)
        >>> beta = np.std(maxima) * np.sqrt(6) / np.pi
        >>> mu = np.mean(maxima) - 0.57721*beta
        >>> plt.plot(bins, (1/beta)*np.exp(-(bins - mu)/beta)
        ...          * np.exp(-np.exp(-(bins - mu)/beta)),
        ...          linewidth=2, color='r')
        >>> plt.plot(bins, 1/(beta * np.sqrt(2 * np.pi))
        ...          * np.exp(-(bins - mu)**2 / (2 * beta**2)),
        ...          linewidth=2, color='g')
        >>> plt.show()