Module « numpy.random »

Fonction rayleigh - module numpy.random

Signature de la fonction rayleigh

Description

rayleigh.__doc__

        rayleigh(scale=1.0, size=None)

        Draw samples from a Rayleigh distribution.

        The :math:`\chi` and Weibull distributions are generalizations of the
        Rayleigh.

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

        Parameters
        ----------
        scale : float or array_like of floats, optional
            Scale, also equals the mode. Must be non-negative. Default is 1.
        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 ``scale`` is a scalar.  Otherwise,
            ``np.array(scale).size`` samples are drawn.

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

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

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

        .. math:: P(x;scale) = \frac{x}{scale^2}e^{\frac{-x^2}{2 \cdotp scale^2}}

        The Rayleigh distribution would arise, for example, if the East
        and North components of the wind velocity had identical zero-mean
        Gaussian distributions.  Then the wind speed would have a Rayleigh
        distribution.

        References
        ----------
        .. [1] Brighton Webs Ltd., "Rayleigh Distribution,"
               https://web.archive.org/web/20090514091424/http://brighton-webs.co.uk:80/distributions/rayleigh.asp
        .. [2] Wikipedia, "Rayleigh distribution"
               https://en.wikipedia.org/wiki/Rayleigh_distribution

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

        >>> from matplotlib.pyplot import hist
        >>> values = hist(np.random.rayleigh(3, 100000), bins=200, density=True)

        Wave heights tend to follow a Rayleigh distribution. If the mean wave
        height is 1 meter, what fraction of waves are likely to be larger than 3
        meters?

        >>> meanvalue = 1
        >>> modevalue = np.sqrt(2 / np.pi) * meanvalue
        >>> s = np.random.rayleigh(modevalue, 1000000)

        The percentage of waves larger than 3 meters is:

        >>> 100.*sum(s>3)/1000000.
        0.087300000000000003 # random