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_distn_infrastructure.py
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_distn_infrastructure.py
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#
# Author: Travis Oliphant 2002-2011 with contributions from
# SciPy Developers 2004-2011
#
from __future__ import division, print_function, absolute_import
from scipy._lib.six import string_types, exec_, PY3
from scipy._lib._util import getargspec_no_self as _getargspec
import sys
import keyword
import re
import types
import warnings
from scipy.misc import doccer
from ._distr_params import distcont, distdiscrete
from scipy._lib._util import check_random_state, _lazywhere, _lazyselect
from scipy._lib._util import _valarray as valarray
from scipy.special import (comb, chndtr, entr, rel_entr, kl_div, xlogy, ive)
# for root finding for discrete distribution ppf, and max likelihood estimation
from scipy import optimize
# for functions of continuous distributions (e.g. moments, entropy, cdf)
from scipy import integrate
# to approximate the pdf of a continuous distribution given its cdf
from scipy.misc import derivative
from numpy import (arange, putmask, ravel, take, ones, shape, ndarray,
product, reshape, zeros, floor, logical_and, log, sqrt, exp)
from numpy import (place, argsort, argmax, vectorize,
asarray, nan, inf, isinf, NINF, empty)
import numpy as np
from ._constants import _XMAX
if PY3:
def instancemethod(func, obj, cls):
return types.MethodType(func, obj)
else:
instancemethod = types.MethodType
# These are the docstring parts used for substitution in specific
# distribution docstrings
docheaders = {'methods': """\nMethods\n-------\n""",
'notes': """\nNotes\n-----\n""",
'examples': """\nExamples\n--------\n"""}
_doc_rvs = """\
``rvs(%(shapes)s, loc=0, scale=1, size=1, random_state=None)``
Random variates.
"""
_doc_pdf = """\
``pdf(x, %(shapes)s, loc=0, scale=1)``
Probability density function.
"""
_doc_logpdf = """\
``logpdf(x, %(shapes)s, loc=0, scale=1)``
Log of the probability density function.
"""
_doc_pmf = """\
``pmf(k, %(shapes)s, loc=0, scale=1)``
Probability mass function.
"""
_doc_logpmf = """\
``logpmf(k, %(shapes)s, loc=0, scale=1)``
Log of the probability mass function.
"""
_doc_cdf = """\
``cdf(x, %(shapes)s, loc=0, scale=1)``
Cumulative distribution function.
"""
_doc_logcdf = """\
``logcdf(x, %(shapes)s, loc=0, scale=1)``
Log of the cumulative distribution function.
"""
_doc_sf = """\
``sf(x, %(shapes)s, loc=0, scale=1)``
Survival function (also defined as ``1 - cdf``, but `sf` is sometimes more accurate).
"""
_doc_logsf = """\
``logsf(x, %(shapes)s, loc=0, scale=1)``
Log of the survival function.
"""
_doc_ppf = """\
``ppf(q, %(shapes)s, loc=0, scale=1)``
Percent point function (inverse of ``cdf`` --- percentiles).
"""
_doc_isf = """\
``isf(q, %(shapes)s, loc=0, scale=1)``
Inverse survival function (inverse of ``sf``).
"""
_doc_moment = """\
``moment(n, %(shapes)s, loc=0, scale=1)``
Non-central moment of order n
"""
_doc_stats = """\
``stats(%(shapes)s, loc=0, scale=1, moments='mv')``
Mean('m'), variance('v'), skew('s'), and/or kurtosis('k').
"""
_doc_entropy = """\
``entropy(%(shapes)s, loc=0, scale=1)``
(Differential) entropy of the RV.
"""
_doc_fit = """\
``fit(data, %(shapes)s, loc=0, scale=1)``
Parameter estimates for generic data.
"""
_doc_expect = """\
``expect(func, args=(%(shapes_)s), loc=0, scale=1, lb=None, ub=None, conditional=False, **kwds)``
Expected value of a function (of one argument) with respect to the distribution.
"""
_doc_expect_discrete = """\
``expect(func, args=(%(shapes_)s), loc=0, lb=None, ub=None, conditional=False)``
Expected value of a function (of one argument) with respect to the distribution.
"""
_doc_median = """\
``median(%(shapes)s, loc=0, scale=1)``
Median of the distribution.
"""
_doc_mean = """\
``mean(%(shapes)s, loc=0, scale=1)``
Mean of the distribution.
"""
_doc_var = """\
``var(%(shapes)s, loc=0, scale=1)``
Variance of the distribution.
"""
_doc_std = """\
``std(%(shapes)s, loc=0, scale=1)``
Standard deviation of the distribution.
"""
_doc_interval = """\
``interval(alpha, %(shapes)s, loc=0, scale=1)``
Endpoints of the range that contains alpha percent of the distribution
"""
_doc_allmethods = ''.join([docheaders['methods'], _doc_rvs, _doc_pdf,
_doc_logpdf, _doc_cdf, _doc_logcdf, _doc_sf,
_doc_logsf, _doc_ppf, _doc_isf, _doc_moment,
_doc_stats, _doc_entropy, _doc_fit,
_doc_expect, _doc_median,
_doc_mean, _doc_var, _doc_std, _doc_interval])
_doc_default_longsummary = """\
As an instance of the `rv_continuous` class, `%(name)s` 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.
"""
_doc_default_frozen_note = """
Alternatively, the object may be called (as a function) to fix the shape,
location, and scale parameters returning a "frozen" continuous RV object:
rv = %(name)s(%(shapes)s, loc=0, scale=1)
- Frozen RV object with the same methods but holding the given shape,
location, and scale fixed.
"""
_doc_default_example = """\
Examples
--------
>>> from scipy.stats import %(name)s
>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots(1, 1)
Calculate a few first moments:
%(set_vals_stmt)s
>>> mean, var, skew, kurt = %(name)s.stats(%(shapes)s, moments='mvsk')
Display the probability density function (``pdf``):
>>> x = np.linspace(%(name)s.ppf(0.01, %(shapes)s),
... %(name)s.ppf(0.99, %(shapes)s), 100)
>>> ax.plot(x, %(name)s.pdf(x, %(shapes)s),
... 'r-', lw=5, alpha=0.6, label='%(name)s 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 = %(name)s(%(shapes)s)
>>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf')
Check accuracy of ``cdf`` and ``ppf``:
>>> vals = %(name)s.ppf([0.001, 0.5, 0.999], %(shapes)s)
>>> np.allclose([0.001, 0.5, 0.999], %(name)s.cdf(vals, %(shapes)s))
True
Generate random numbers:
>>> r = %(name)s.rvs(%(shapes)s, size=1000)
And compare the histogram:
>>> ax.hist(r, normed=True, histtype='stepfilled', alpha=0.2)
>>> ax.legend(loc='best', frameon=False)
>>> plt.show()
"""
_doc_default_locscale = """\
The probability density above is defined in the "standardized" form. To shift
and/or scale the distribution use the ``loc`` and ``scale`` parameters.
Specifically, ``%(name)s.pdf(x, %(shapes)s, loc, scale)`` is identically
equivalent to ``%(name)s.pdf(y, %(shapes)s) / scale`` with
``y = (x - loc) / scale``.
"""
_doc_default = ''.join([_doc_default_longsummary,
_doc_allmethods,
'\n',
_doc_default_example])
_doc_default_before_notes = ''.join([_doc_default_longsummary,
_doc_allmethods])
docdict = {
'rvs': _doc_rvs,
'pdf': _doc_pdf,
'logpdf': _doc_logpdf,
'cdf': _doc_cdf,
'logcdf': _doc_logcdf,
'sf': _doc_sf,
'logsf': _doc_logsf,
'ppf': _doc_ppf,
'isf': _doc_isf,
'stats': _doc_stats,
'entropy': _doc_entropy,
'fit': _doc_fit,
'moment': _doc_moment,
'expect': _doc_expect,
'interval': _doc_interval,
'mean': _doc_mean,
'std': _doc_std,
'var': _doc_var,
'median': _doc_median,
'allmethods': _doc_allmethods,
'longsummary': _doc_default_longsummary,
'frozennote': _doc_default_frozen_note,
'example': _doc_default_example,
'default': _doc_default,
'before_notes': _doc_default_before_notes,
'after_notes': _doc_default_locscale
}
# Reuse common content between continuous and discrete docs, change some
# minor bits.
docdict_discrete = docdict.copy()
docdict_discrete['pmf'] = _doc_pmf
docdict_discrete['logpmf'] = _doc_logpmf
docdict_discrete['expect'] = _doc_expect_discrete
_doc_disc_methods = ['rvs', 'pmf', 'logpmf', 'cdf', 'logcdf', 'sf', 'logsf',
'ppf', 'isf', 'stats', 'entropy', 'expect', 'median',
'mean', 'var', 'std', 'interval']
for obj in _doc_disc_methods:
docdict_discrete[obj] = docdict_discrete[obj].replace(', scale=1', '')
_doc_disc_methods_err_varname = ['cdf', 'logcdf', 'sf', 'logsf']
for obj in _doc_disc_methods_err_varname:
docdict_discrete[obj] = docdict_discrete[obj].replace('(x, ', '(k, ')
docdict_discrete.pop('pdf')
docdict_discrete.pop('logpdf')
_doc_allmethods = ''.join([docdict_discrete[obj] for obj in _doc_disc_methods])
docdict_discrete['allmethods'] = docheaders['methods'] + _doc_allmethods
docdict_discrete['longsummary'] = _doc_default_longsummary.replace(
'rv_continuous', 'rv_discrete')
_doc_default_frozen_note = """
Alternatively, the object may be called (as a function) to fix the shape and
location parameters returning a "frozen" discrete RV object:
rv = %(name)s(%(shapes)s, loc=0)
- Frozen RV object with the same methods but holding the given shape and
location fixed.
"""
docdict_discrete['frozennote'] = _doc_default_frozen_note
_doc_default_discrete_example = """\
Examples
--------
>>> from scipy.stats import %(name)s
>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots(1, 1)
Calculate a few first moments:
%(set_vals_stmt)s
>>> mean, var, skew, kurt = %(name)s.stats(%(shapes)s, moments='mvsk')
Display the probability mass function (``pmf``):
>>> x = np.arange(%(name)s.ppf(0.01, %(shapes)s),
... %(name)s.ppf(0.99, %(shapes)s))
>>> ax.plot(x, %(name)s.pmf(x, %(shapes)s), 'bo', ms=8, label='%(name)s pmf')
>>> ax.vlines(x, 0, %(name)s.pmf(x, %(shapes)s), 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 = %(name)s(%(shapes)s)
>>> 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 = %(name)s.cdf(x, %(shapes)s)
>>> np.allclose(x, %(name)s.ppf(prob, %(shapes)s))
True
Generate random numbers:
>>> r = %(name)s.rvs(%(shapes)s, size=1000)
"""
_doc_default_discrete_locscale = """\
The probability mass function above is defined in the "standardized" form.
To shift distribution use the ``loc`` parameter.
Specifically, ``%(name)s.pmf(k, %(shapes)s, loc)`` is identically
equivalent to ``%(name)s.pmf(k - loc, %(shapes)s)``.
"""
docdict_discrete['example'] = _doc_default_discrete_example
docdict_discrete['after_notes'] = _doc_default_discrete_locscale
_doc_default_before_notes = ''.join([docdict_discrete['longsummary'],
docdict_discrete['allmethods']])
docdict_discrete['before_notes'] = _doc_default_before_notes
_doc_default_disc = ''.join([docdict_discrete['longsummary'],
docdict_discrete['allmethods'],
docdict_discrete['frozennote'],
docdict_discrete['example']])
docdict_discrete['default'] = _doc_default_disc
# clean up all the separate docstring elements, we do not need them anymore
for obj in [s for s in dir() if s.startswith('_doc_')]:
exec('del ' + obj)
del obj
try:
del s
except NameError:
# in Python 3, loop variables are not visible after the loop
pass
def _moment(data, n, mu=None):
if mu is None:
mu = data.mean()
return ((data - mu)**n).mean()
def _moment_from_stats(n, mu, mu2, g1, g2, moment_func, args):
if (n == 0):
return 1.0
elif (n == 1):
if mu is None:
val = moment_func(1, *args)
else:
val = mu
elif (n == 2):
if mu2 is None or mu is None:
val = moment_func(2, *args)
else:
val = mu2 + mu*mu
elif (n == 3):
if g1 is None or mu2 is None or mu is None:
val = moment_func(3, *args)
else:
mu3 = g1 * np.power(mu2, 1.5) # 3rd central moment
val = mu3+3*mu*mu2+mu*mu*mu # 3rd non-central moment
elif (n == 4):
if g1 is None or g2 is None or mu2 is None or mu is None:
val = moment_func(4, *args)
else:
mu4 = (g2+3.0)*(mu2**2.0) # 4th central moment
mu3 = g1*np.power(mu2, 1.5) # 3rd central moment
val = mu4+4*mu*mu3+6*mu*mu*mu2+mu*mu*mu*mu
else:
val = moment_func(n, *args)
return val
def _skew(data):
"""
skew is third central moment / variance**(1.5)
"""
data = np.ravel(data)
mu = data.mean()
m2 = ((data - mu)**2).mean()
m3 = ((data - mu)**3).mean()
return m3 / np.power(m2, 1.5)
def _kurtosis(data):
"""
kurtosis is fourth central moment / variance**2 - 3
"""
data = np.ravel(data)
mu = data.mean()
m2 = ((data - mu)**2).mean()
m4 = ((data - mu)**4).mean()
return m4 / m2**2 - 3
# Frozen RV class
class rv_frozen(object):
def __init__(self, dist, *args, **kwds):
self.args = args
self.kwds = kwds
# create a new instance
self.dist = dist.__class__(**dist._updated_ctor_param())
# a, b may be set in _argcheck, depending on *args, **kwds. Ouch.
shapes, _, _ = self.dist._parse_args(*args, **kwds)
self.dist._argcheck(*shapes)
self.a, self.b = self.dist.a, self.dist.b
@property
def random_state(self):
return self.dist._random_state
@random_state.setter
def random_state(self, seed):
self.dist._random_state = check_random_state(seed)
def pdf(self, x): # raises AttributeError in frozen discrete distribution
return self.dist.pdf(x, *self.args, **self.kwds)
def logpdf(self, x):
return self.dist.logpdf(x, *self.args, **self.kwds)
def cdf(self, x):
return self.dist.cdf(x, *self.args, **self.kwds)
def logcdf(self, x):
return self.dist.logcdf(x, *self.args, **self.kwds)
def ppf(self, q):
return self.dist.ppf(q, *self.args, **self.kwds)
def isf(self, q):
return self.dist.isf(q, *self.args, **self.kwds)
def rvs(self, size=None, random_state=None):
kwds = self.kwds.copy()
kwds.update({'size': size, 'random_state': random_state})
return self.dist.rvs(*self.args, **kwds)
def sf(self, x):
return self.dist.sf(x, *self.args, **self.kwds)
def logsf(self, x):
return self.dist.logsf(x, *self.args, **self.kwds)
def stats(self, moments='mv'):
kwds = self.kwds.copy()
kwds.update({'moments': moments})
return self.dist.stats(*self.args, **kwds)
def median(self):
return self.dist.median(*self.args, **self.kwds)
def mean(self):
return self.dist.mean(*self.args, **self.kwds)
def var(self):
return self.dist.var(*self.args, **self.kwds)
def std(self):
return self.dist.std(*self.args, **self.kwds)
def moment(self, n):
return self.dist.moment(n, *self.args, **self.kwds)
def entropy(self):
return self.dist.entropy(*self.args, **self.kwds)
def pmf(self, k):
return self.dist.pmf(k, *self.args, **self.kwds)
def logpmf(self, k):
return self.dist.logpmf(k, *self.args, **self.kwds)
def interval(self, alpha):
return self.dist.interval(alpha, *self.args, **self.kwds)
def expect(self, func=None, lb=None, ub=None, conditional=False, **kwds):
# expect method only accepts shape parameters as positional args
# hence convert self.args, self.kwds, also loc/scale
# See the .expect method docstrings for the meaning of
# other parameters.
a, loc, scale = self.dist._parse_args(*self.args, **self.kwds)
if isinstance(self.dist, rv_discrete):
return self.dist.expect(func, a, loc, lb, ub, conditional, **kwds)
else:
return self.dist.expect(func, a, loc, scale, lb, ub,
conditional, **kwds)
# This should be rewritten
def argsreduce(cond, *args):
"""Return the sequence of ravel(args[i]) where ravel(condition) is
True in 1D.
Examples
--------
>>> import numpy as np
>>> rand = np.random.random_sample
>>> A = rand((4, 5))
>>> B = 2
>>> C = rand((1, 5))
>>> cond = np.ones(A.shape)
>>> [A1, B1, C1] = argsreduce(cond, A, B, C)
>>> B1.shape
(20,)
>>> cond[2,:] = 0
>>> [A2, B2, C2] = argsreduce(cond, A, B, C)
>>> B2.shape
(15,)
"""
newargs = np.atleast_1d(*args)
if not isinstance(newargs, list):
newargs = [newargs, ]
expand_arr = (cond == cond)
return [np.extract(cond, arr1 * expand_arr) for arr1 in newargs]
parse_arg_template = """
def _parse_args(self, %(shape_arg_str)s %(locscale_in)s):
return (%(shape_arg_str)s), %(locscale_out)s
def _parse_args_rvs(self, %(shape_arg_str)s %(locscale_in)s, size=None):
return self._argcheck_rvs(%(shape_arg_str)s %(locscale_out)s, size=size)
def _parse_args_stats(self, %(shape_arg_str)s %(locscale_in)s, moments='mv'):
return (%(shape_arg_str)s), %(locscale_out)s, moments
"""
# Both the continuous and discrete distributions depend on ncx2.
# I think the function name ncx2 is an abbreviation for noncentral chi squared.
def _ncx2_log_pdf(x, df, nc):
# We use (xs**2 + ns**2)/2 = (xs - ns)**2/2 + xs*ns, and include the factor
# of exp(-xs*ns) into the ive function to improve numerical stability
# at large values of xs. See also `rice.pdf`.
df2 = df/2.0 - 1.0
xs, ns = np.sqrt(x), np.sqrt(nc)
res = xlogy(df2/2.0, x/nc) - 0.5*(xs - ns)**2
res += np.log(ive(df2, xs*ns) / 2.0)
return res
def _ncx2_pdf(x, df, nc):
return np.exp(_ncx2_log_pdf(x, df, nc))
def _ncx2_cdf(x, df, nc):
return chndtr(x, df, nc)
class rv_generic(object):
"""Class which encapsulates common functionality between rv_discrete
and rv_continuous.
"""
def __init__(self, seed=None):
super(rv_generic, self).__init__()
# figure out if _stats signature has 'moments' keyword
sign = _getargspec(self._stats)
self._stats_has_moments = ((sign[2] is not None) or
('moments' in sign[0]))
self._random_state = check_random_state(seed)
@property
def random_state(self):
""" Get or set the RandomState object for generating random variates.
This can be either None or an existing RandomState object.
If None (or np.random), use the RandomState singleton used by np.random.
If already a RandomState instance, use it.
If an int, use a new RandomState instance seeded with seed.
"""
return self._random_state
@random_state.setter
def random_state(self, seed):
self._random_state = check_random_state(seed)
def __getstate__(self):
return self._updated_ctor_param(), self._random_state
def __setstate__(self, state):
ctor_param, r = state
self.__init__(**ctor_param)
self._random_state = r
return self
def _construct_argparser(
self, meths_to_inspect, locscale_in, locscale_out):
"""Construct the parser for the shape arguments.
Generates the argument-parsing functions dynamically and attaches
them to the instance.
Is supposed to be called in __init__ of a class for each distribution.
If self.shapes is a non-empty string, interprets it as a
comma-separated list of shape parameters.
Otherwise inspects the call signatures of `meths_to_inspect`
and constructs the argument-parsing functions from these.
In this case also sets `shapes` and `numargs`.
"""
if self.shapes:
# sanitize the user-supplied shapes
if not isinstance(self.shapes, string_types):
raise TypeError('shapes must be a string.')
shapes = self.shapes.replace(',', ' ').split()
for field in shapes:
if keyword.iskeyword(field):
raise SyntaxError('keywords cannot be used as shapes.')
if not re.match('^[_a-zA-Z][_a-zA-Z0-9]*$', field):
raise SyntaxError(
'shapes must be valid python identifiers')
else:
# find out the call signatures (_pdf, _cdf etc), deduce shape
# arguments. Generic methods only have 'self, x', any further args
# are shapes.
shapes_list = []
for meth in meths_to_inspect:
shapes_args = _getargspec(meth) # NB: does not contain self
args = shapes_args.args[1:] # peel off 'x', too
if args:
shapes_list.append(args)
# *args or **kwargs are not allowed w/automatic shapes
if shapes_args.varargs is not None:
raise TypeError(
'*args are not allowed w/out explicit shapes')
if shapes_args.keywords is not None:
raise TypeError(
'**kwds are not allowed w/out explicit shapes')
if shapes_args.defaults is not None:
raise TypeError('defaults are not allowed for shapes')
if shapes_list:
shapes = shapes_list[0]
# make sure the signatures are consistent
for item in shapes_list:
if item != shapes:
raise TypeError('Shape arguments are inconsistent.')
else:
shapes = []
# have the arguments, construct the method from template
shapes_str = ', '.join(shapes) + ', ' if shapes else '' # NB: not None
dct = dict(shape_arg_str=shapes_str,
locscale_in=locscale_in,
locscale_out=locscale_out,
)
ns = {}
exec_(parse_arg_template % dct, ns)
# NB: attach to the instance, not class
for name in ['_parse_args', '_parse_args_stats', '_parse_args_rvs']:
setattr(self, name,
instancemethod(ns[name], self, self.__class__)
)
self.shapes = ', '.join(shapes) if shapes else None
if not hasattr(self, 'numargs'):
# allows more general subclassing with *args
self.numargs = len(shapes)
def _construct_doc(self, docdict, shapes_vals=None):
"""Construct the instance docstring with string substitutions."""
tempdict = docdict.copy()
tempdict['name'] = self.name or 'distname'
tempdict['shapes'] = self.shapes or ''
if shapes_vals is None:
shapes_vals = ()
vals = ', '.join('%.3g' % val for val in shapes_vals)
tempdict['vals'] = vals
tempdict['shapes_'] = self.shapes or ''
if self.shapes and self.numargs == 1:
tempdict['shapes_'] += ','
if self.shapes:
tempdict['set_vals_stmt'] = '>>> %s = %s' % (self.shapes, vals)
else:
tempdict['set_vals_stmt'] = ''
if self.shapes is None:
# remove shapes from call parameters if there are none
for item in ['default', 'before_notes']:
tempdict[item] = tempdict[item].replace(
"\n%(shapes)s : array_like\n shape parameters", "")
for i in range(2):
if self.shapes is None:
# necessary because we use %(shapes)s in two forms (w w/o ", ")
self.__doc__ = self.__doc__.replace("%(shapes)s, ", "")
self.__doc__ = doccer.docformat(self.__doc__, tempdict)
# correct for empty shapes
self.__doc__ = self.__doc__.replace('(, ', '(').replace(', )', ')')
def _construct_default_doc(self, longname=None, extradoc=None,
docdict=None, discrete='continuous'):
"""Construct instance docstring from the default template."""
if longname is None:
longname = 'A'
if extradoc is None:
extradoc = ''
if extradoc.startswith('\n\n'):
extradoc = extradoc[2:]
self.__doc__ = ''.join(['%s %s random variable.' % (longname, discrete),
'\n\n%(before_notes)s\n', docheaders['notes'],
extradoc, '\n%(example)s'])
self._construct_doc(docdict)
def freeze(self, *args, **kwds):
"""Freeze the distribution for the given arguments.
Parameters
----------
arg1, arg2, arg3,... : array_like
The shape parameter(s) for the distribution. Should include all
the non-optional arguments, may include ``loc`` and ``scale``.
Returns
-------
rv_frozen : rv_frozen instance
The frozen distribution.
"""
return rv_frozen(self, *args, **kwds)
def __call__(self, *args, **kwds):
return self.freeze(*args, **kwds)
__call__.__doc__ = freeze.__doc__
# The actual calculation functions (no basic checking need be done)
# If these are defined, the others won't be looked at.
# Otherwise, the other set can be defined.
def _stats(self, *args, **kwds):
return None, None, None, None
# Central moments
def _munp(self, n, *args):
# Silence floating point warnings from integration.
olderr = np.seterr(all='ignore')
vals = self.generic_moment(n, *args)
np.seterr(**olderr)
return vals
def _argcheck_rvs(self, *args, **kwargs):
# Handle broadcasting and size validation of the rvs method.
# Subclasses should not have to override this method.
# The rule is that if `size` is not None, then `size` gives the
# shape of the result (integer values of `size` are treated as
# tuples with length 1; i.e. `size=3` is the same as `size=(3,)`.)
#
# `args` is expected to contain the shape parameters (if any), the
# location and the scale in a flat tuple (e.g. if there are two
# shape parameters `a` and `b`, `args` will be `(a, b, loc, scale)`).
# The only keyword argument expected is 'size'.
size = kwargs.get('size', None)
all_bcast = np.broadcast_arrays(*args)
def squeeze_left(a):
while a.ndim > 0 and a.shape[0] == 1:
a = a[0]
return a
# Eliminate trivial leading dimensions. In the convention
# used by numpy's random variate generators, trivial leading
# dimensions are effectively ignored. In other words, when `size`
# is given, trivial leading dimensions of the broadcast parameters
# in excess of the number of dimensions in size are ignored, e.g.
# >>> np.random.normal([[1, 3, 5]], [[[[0.01]]]], size=3)
# array([ 1.00104267, 3.00422496, 4.99799278])
# If `size` is not given, the exact broadcast shape is preserved:
# >>> np.random.normal([[1, 3, 5]], [[[[0.01]]]])
# array([[[[ 1.00862899, 3.00061431, 4.99867122]]]])
#
all_bcast = [squeeze_left(a) for a in all_bcast]
bcast_shape = all_bcast[0].shape
bcast_ndim = all_bcast[0].ndim
if size is None:
size_ = bcast_shape
else:
size_ = tuple(np.atleast_1d(size))
# Check compatibility of size_ with the broadcast shape of all
# the parameters. This check is intended to be consistent with
# how the numpy random variate generators (e.g. np.random.normal,
# np.random.beta) handle their arguments. The rule is that, if size
# is given, it determines the shape of the output. Broadcasting
# can't change the output size.
# This is the standard broadcasting convention of extending the
# shape with fewer dimensions with enough dimensions of length 1
# so that the two shapes have the same number of dimensions.
ndiff = bcast_ndim - len(size_)
if ndiff < 0:
bcast_shape = (1,)*(-ndiff) + bcast_shape
elif ndiff > 0:
size_ = (1,)*ndiff + size_
# This compatibility test is not standard. In "regular" broadcasting,
# two shapes are compatible if for each dimension, the lengths are the
# same or one of the lengths is 1. Here, the length of a dimension in
# size_ must not be less than the corresponding length in bcast_shape.
ok = all([bcdim == 1 or bcdim == szdim
for (bcdim, szdim) in zip(bcast_shape, size_)])
if not ok:
raise ValueError("size does not match the broadcast shape of "
"the parameters.")
param_bcast = all_bcast[:-2]
loc_bcast = all_bcast[-2]
scale_bcast = all_bcast[-1]
return param_bcast, loc_bcast, scale_bcast, size_
## These are the methods you must define (standard form functions)
## NB: generic _pdf, _logpdf, _cdf are different for
## rv_continuous and rv_discrete hence are defined in there
def _argcheck(self, *args):
"""Default check for correct values on args and keywords.
Returns condition array of 1's where arguments are correct and
0's where they are not.
"""
cond = 1
for arg in args:
cond = logical_and(cond, (asarray(arg) > 0))
return cond
def _support_mask(self, x):
return (self.a <= x) & (x <= self.b)
def _open_support_mask(self, x):
return (self.a < x) & (x < self.b)
def _rvs(self, *args):
# This method must handle self._size being a tuple, and it must
# properly broadcast *args and self._size. self._size might be
# an empty tuple, which means a scalar random variate is to be
# generated.
## Use basic inverse cdf algorithm for RV generation as default.
U = self._random_state.random_sample(self._size)
Y = self._ppf(U, *args)
return Y
def _logcdf(self, x, *args):
return log(self._cdf(x, *args))
def _sf(self, x, *args):
return 1.0-self._cdf(x, *args)
def _logsf(self, x, *args):
return log(self._sf(x, *args))
def _ppf(self, q, *args):
return self._ppfvec(q, *args)
def _isf(self, q, *args):
return self._ppf(1.0-q, *args) # use correct _ppf for subclasses
# These are actually called, and should not be overwritten if you
# want to keep error checking.
def rvs(self, *args, **kwds):
"""
Random variates of given type.
Parameters
----------
arg1, arg2, arg3,... : array_like
The shape parameter(s) for the distribution (see docstring of the
instance object for more information).
loc : array_like, optional
Location parameter (default=0).
scale : array_like, optional
Scale parameter (default=1).
size : int or tuple of ints, optional
Defining number of random variates (default is 1).
random_state : None or int or ``np.random.RandomState`` instance, optional
If int or RandomState, use it for drawing the random variates.
If None, rely on ``self.random_state``.
Default is None.
Returns
-------
rvs : ndarray or scalar
Random variates of given `size`.
"""
discrete = kwds.pop('discrete', None)
rndm = kwds.pop('random_state', None)
args, loc, scale, size = self._parse_args_rvs(*args, **kwds)
cond = logical_and(self._argcheck(*args), (scale >= 0))
if not np.all(cond):
raise ValueError("Domain error in arguments.")
if np.all(scale == 0):
return loc*ones(size, 'd')
# extra gymnastics needed for a custom random_state
if rndm is not None:
random_state_saved = self._random_state
self._random_state = check_random_state(rndm)
# `size` should just be an argument to _rvs(), but for, um,
# historical reasons, it is made an attribute that is read
# by _rvs().
self._size = size
vals = self._rvs(*args)
vals = vals * scale + loc
# do not forget to restore the _random_state
if rndm is not None:
self._random_state = random_state_saved
# Cast to int if discrete
if discrete:
if size == ():
vals = int(vals)
else:
vals = vals.astype(int)
return vals
def stats(self, *args, **kwds):
"""
Some statistics of the given RV.
Parameters
----------
arg1, arg2, arg3,... : array_like
The shape parameter(s) for the distribution (see docstring of the
instance object for more information)
loc : array_like, optional
location parameter (default=0)
scale : array_like, optional (continuous RVs only)
scale parameter (default=1)
moments : str, optional
composed of letters ['mvsk'] defining which moments to compute:
'm' = mean,
'v' = variance,
's' = (Fisher's) skew,
'k' = (Fisher's) kurtosis.
(default is 'mv')
Returns
-------
stats : sequence
of requested moments.
"""
args, loc, scale, moments = self._parse_args_stats(*args, **kwds)
# scale = 1 by construction for discrete RVs
loc, scale = map(asarray, (loc, scale))