# scipy.stats.burr12#

scipy.stats.burr12 = <scipy.stats._continuous_distns.burr12_gen object>[source]#

A Burr (Type XII) continuous random variable.

As an instance of the rv_continuous class, burr12 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.

fisk

a special case of either burr or burr12 with d=1

burr

Burr Type III distribution

Notes

The probability density function for burr12 is:

$f(x; c, d) = c d \frac{x^{c-1}} {(1 + x^c)^{d + 1}}$

for $$x >= 0$$ and $$c, d > 0$$.

burr12 takes c and d as shape parameters for $$c$$ and $$d$$.

This is the PDF corresponding to the twelfth CDF given in Burr’s list; specifically, it is equation (20) in Burr’s paper .

The probability density above is defined in the “standardized” form. To shift and/or scale the distribution use the loc and scale parameters. Specifically, burr12.pdf(x, c, d, loc, scale) is identically equivalent to burr12.pdf(y, c, d) / scale with y = (x - loc) / scale. Note that shifting the location of a distribution does not make it a “noncentral” distribution; noncentral generalizations of some distributions are available in separate classes.

The Burr type 12 distribution is also sometimes referred to as the Singh-Maddala distribution from NIST .

References



Burr, I. W. “Cumulative frequency functions”, Annals of Mathematical Statistics, 13(2), pp 215-232 (1942).

Examples

>>> import numpy as np
>>> from scipy.stats import burr12
>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots(1, 1)


Calculate the first four moments:

>>> c, d = 10, 4
>>> mean, var, skew, kurt = burr12.stats(c, d, moments='mvsk')


Display the probability density function (pdf):

>>> x = np.linspace(burr12.ppf(0.01, c, d),
...                 burr12.ppf(0.99, c, d), 100)
>>> ax.plot(x, burr12.pdf(x, c, d),
...        'r-', lw=5, alpha=0.6, label='burr12 pdf')


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

Freeze the distribution and display the frozen pdf:

>>> rv = burr12(c, d)
>>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf')


Check accuracy of cdf and ppf:

>>> vals = burr12.ppf([0.001, 0.5, 0.999], c, d)
>>> np.allclose([0.001, 0.5, 0.999], burr12.cdf(vals, c, d))
True


Generate random numbers:

>>> r = burr12.rvs(c, d, size=1000)


And compare the histogram:

>>> ax.hist(r, density=True, bins='auto', histtype='stepfilled', alpha=0.2)
>>> ax.set_xlim([x, x[-1]])
>>> ax.legend(loc='best', frameon=False)
>>> plt.show()


Methods

 rvs(c, d, loc=0, scale=1, size=1, random_state=None) Random variates. pdf(x, c, d, loc=0, scale=1) Probability density function. logpdf(x, c, d, loc=0, scale=1) Log of the probability density function. cdf(x, c, d, loc=0, scale=1) Cumulative distribution function. logcdf(x, c, d, loc=0, scale=1) Log of the cumulative distribution function. sf(x, c, d, loc=0, scale=1) Survival function (also defined as 1 - cdf, but sf is sometimes more accurate). logsf(x, c, d, loc=0, scale=1) Log of the survival function. ppf(q, c, d, loc=0, scale=1) Percent point function (inverse of cdf — percentiles). isf(q, c, d, loc=0, scale=1) Inverse survival function (inverse of sf). moment(order, c, d, loc=0, scale=1) Non-central moment of the specified order. stats(c, d, loc=0, scale=1, moments=’mv’) Mean(‘m’), variance(‘v’), skew(‘s’), and/or kurtosis(‘k’). entropy(c, d, loc=0, scale=1) (Differential) entropy of the RV. fit(data) Parameter estimates for generic data. See scipy.stats.rv_continuous.fit for detailed documentation of the keyword arguments. expect(func, args=(c, d), loc=0, scale=1, lb=None, ub=None, conditional=False, **kwds) Expected value of a function (of one argument) with respect to the distribution. median(c, d, loc=0, scale=1) Median of the distribution. mean(c, d, loc=0, scale=1) Mean of the distribution. var(c, d, loc=0, scale=1) Variance of the distribution. std(c, d, loc=0, scale=1) Standard deviation of the distribution. interval(confidence, c, d, loc=0, scale=1) Confidence interval with equal areas around the median.