# scipy.stats.geom#

scipy.stats.geom = <scipy.stats._discrete_distns.geom_gen object>[source]#

A geometric discrete random variable.

As an instance of the rv_discrete class, geom object inherits from it a collection of generic methods (see below for the full list), and completes them with details specific for this particular distribution.

Notes

The probability mass function for geom is:

$f(k) = (1-p)^{k-1} p$

for $$k \ge 1$$, $$0 < p \leq 1$$

geom takes $$p$$ as shape parameter, where $$p$$ is the probability of a single success and $$1-p$$ is the probability of a single failure.

The probability mass function above is defined in the “standardized” form. To shift distribution use the loc parameter. Specifically, geom.pmf(k, p, loc) is identically equivalent to geom.pmf(k - loc, p).

Examples

>>> import numpy as np
>>> from scipy.stats import geom
>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots(1, 1)


Calculate the first four moments:

>>> p = 0.5
>>> mean, var, skew, kurt = geom.stats(p, moments='mvsk')


Display the probability mass function (pmf):

>>> x = np.arange(geom.ppf(0.01, p),
...               geom.ppf(0.99, p))
>>> ax.plot(x, geom.pmf(x, p), 'bo', ms=8, label='geom pmf')
>>> ax.vlines(x, 0, geom.pmf(x, p), colors='b', lw=5, alpha=0.5)


Alternatively, the distribution object can be called (as a function) to fix the shape and location. This returns a “frozen” RV object holding the given parameters fixed.

Freeze the distribution and display the frozen pmf:

>>> rv = geom(p)
>>> ax.vlines(x, 0, rv.pmf(x), colors='k', linestyles='-', lw=1,
...         label='frozen pmf')
>>> ax.legend(loc='best', frameon=False)
>>> plt.show()


Check accuracy of cdf and ppf:

>>> prob = geom.cdf(x, p)
>>> np.allclose(x, geom.ppf(prob, p))
True


Generate random numbers:

>>> r = geom.rvs(p, size=1000)


Methods

 rvs(p, loc=0, size=1, random_state=None) Random variates. pmf(k, p, loc=0) Probability mass function. logpmf(k, p, loc=0) Log of the probability mass function. cdf(k, p, loc=0) Cumulative distribution function. logcdf(k, p, loc=0) Log of the cumulative distribution function. sf(k, p, loc=0) Survival function (also defined as 1 - cdf, but sf is sometimes more accurate). logsf(k, p, loc=0) Log of the survival function. ppf(q, p, loc=0) Percent point function (inverse of cdf — percentiles). isf(q, p, loc=0) Inverse survival function (inverse of sf). stats(p, loc=0, moments=’mv’) Mean(‘m’), variance(‘v’), skew(‘s’), and/or kurtosis(‘k’). entropy(p, loc=0) (Differential) entropy of the RV. expect(func, args=(p,), loc=0, lb=None, ub=None, conditional=False) Expected value of a function (of one argument) with respect to the distribution. median(p, loc=0) Median of the distribution. mean(p, loc=0) Mean of the distribution. var(p, loc=0) Variance of the distribution. std(p, loc=0) Standard deviation of the distribution. interval(confidence, p, loc=0) Confidence interval with equal areas around the median.