Module « numpy.random »

Fonction negative_binomial - module numpy.random

Signature de la fonction negative_binomial

Description

negative_binomial.__doc__

        negative_binomial(n, p, size=None)

        Draw samples from a negative binomial distribution.

        Samples are drawn from a negative binomial distribution with specified
        parameters, `n` successes and `p` probability of success where `n`
        is > 0 and `p` is in the interval [0, 1].

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

        Parameters
        ----------
        n : float or array_like of floats
            Parameter of the distribution, > 0.
        p : float or array_like of floats
            Parameter of the distribution, >= 0 and <=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 ``n`` and ``p`` are both scalars.
            Otherwise, ``np.broadcast(n, p).size`` samples are drawn.

        Returns
        -------
        out : ndarray or scalar
            Drawn samples from the parameterized negative binomial distribution,
            where each sample is equal to N, the number of failures that
            occurred before a total of n successes was reached.

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

        Notes
        -----
        The probability mass function of the negative binomial distribution is

        .. math:: P(N;n,p) = \frac{\Gamma(N+n)}{N!\Gamma(n)}p^{n}(1-p)^{N},

        where :math:`n` is the number of successes, :math:`p` is the
        probability of success, :math:`N+n` is the number of trials, and
        :math:`\Gamma` is the gamma function. When :math:`n` is an integer,
        :math:`\frac{\Gamma(N+n)}{N!\Gamma(n)} = \binom{N+n-1}{N}`, which is
        the more common form of this term in the the pmf. The negative
        binomial distribution gives the probability of N failures given n
        successes, with a success on the last trial.

        If one throws a die repeatedly until the third time a "1" appears,
        then the probability distribution of the number of non-"1"s that
        appear before the third "1" is a negative binomial distribution.

        References
        ----------
        .. [1] Weisstein, Eric W. "Negative Binomial Distribution." From
               MathWorld--A Wolfram Web Resource.
               http://mathworld.wolfram.com/NegativeBinomialDistribution.html
        .. [2] Wikipedia, "Negative binomial distribution",
               https://en.wikipedia.org/wiki/Negative_binomial_distribution

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

        A real world example. A company drills wild-cat oil
        exploration wells, each with an estimated probability of
        success of 0.1.  What is the probability of having one success
        for each successive well, that is what is the probability of a
        single success after drilling 5 wells, after 6 wells, etc.?

        >>> s = np.random.negative_binomial(1, 0.1, 100000)
        >>> for i in range(1, 11): # doctest: +SKIP
        ...    probability = sum(s<i) / 100000.
        ...    print(i, "wells drilled, probability of one success =", probability)