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eaiaiaiaoi/venv/lib/python2.7/site-packages/scipy/stats/_multivariate.py

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#
# Author: Joris Vankerschaver 2013
#
from __future__ import division, print_function, absolute_import
import math
import numpy as np
from numpy import asarray_chkfinite, asarray
import scipy.linalg
from scipy.misc import doccer
from scipy.special import gammaln, psi, multigammaln, xlogy, entr
from scipy._lib._util import check_random_state
from scipy.linalg.blas import drot
from scipy.linalg.misc import LinAlgError
from scipy.linalg.lapack import get_lapack_funcs
from ._discrete_distns import binom
from . import mvn
__all__ = ['multivariate_normal',
'matrix_normal',
'dirichlet',
'wishart',
'invwishart',
'multinomial',
'special_ortho_group',
'ortho_group',
'random_correlation',
'unitary_group']
_LOG_2PI = np.log(2 * np.pi)
_LOG_2 = np.log(2)
_LOG_PI = np.log(np.pi)
_doc_random_state = """\
random_state : None or int or np.random.RandomState instance, optional
If int or RandomState, use it for drawing the random variates.
If None (or np.random), the global np.random state is used.
Default is None.
"""
def _squeeze_output(out):
"""
Remove single-dimensional entries from array and convert to scalar,
if necessary.
"""
out = out.squeeze()
if out.ndim == 0:
out = out[()]
return out
def _eigvalsh_to_eps(spectrum, cond=None, rcond=None):
"""
Determine which eigenvalues are "small" given the spectrum.
This is for compatibility across various linear algebra functions
that should agree about whether or not a Hermitian matrix is numerically
singular and what is its numerical matrix rank.
This is designed to be compatible with scipy.linalg.pinvh.
Parameters
----------
spectrum : 1d ndarray
Array of eigenvalues of a Hermitian matrix.
cond, rcond : float, optional
Cutoff for small eigenvalues.
Singular values smaller than rcond * largest_eigenvalue are
considered zero.
If None or -1, suitable machine precision is used.
Returns
-------
eps : float
Magnitude cutoff for numerical negligibility.
"""
if rcond is not None:
cond = rcond
if cond in [None, -1]:
t = spectrum.dtype.char.lower()
factor = {'f': 1E3, 'd': 1E6}
cond = factor[t] * np.finfo(t).eps
eps = cond * np.max(abs(spectrum))
return eps
def _pinv_1d(v, eps=1e-5):
"""
A helper function for computing the pseudoinverse.
Parameters
----------
v : iterable of numbers
This may be thought of as a vector of eigenvalues or singular values.
eps : float
Values with magnitude no greater than eps are considered negligible.
Returns
-------
v_pinv : 1d float ndarray
A vector of pseudo-inverted numbers.
"""
return np.array([0 if abs(x) <= eps else 1/x for x in v], dtype=float)
class _PSD(object):
"""
Compute coordinated functions of a symmetric positive semidefinite matrix.
This class addresses two issues. Firstly it allows the pseudoinverse,
the logarithm of the pseudo-determinant, and the rank of the matrix
to be computed using one call to eigh instead of three.
Secondly it allows these functions to be computed in a way
that gives mutually compatible results.
All of the functions are computed with a common understanding as to
which of the eigenvalues are to be considered negligibly small.
The functions are designed to coordinate with scipy.linalg.pinvh()
but not necessarily with np.linalg.det() or with np.linalg.matrix_rank().
Parameters
----------
M : array_like
Symmetric positive semidefinite matrix (2-D).
cond, rcond : float, optional
Cutoff for small eigenvalues.
Singular values smaller than rcond * largest_eigenvalue are
considered zero.
If None or -1, suitable machine precision is used.
lower : bool, optional
Whether the pertinent array data is taken from the lower
or upper triangle of M. (Default: lower)
check_finite : bool, optional
Whether to check that the input matrices contain only finite
numbers. Disabling may give a performance gain, but may result
in problems (crashes, non-termination) if the inputs do contain
infinities or NaNs.
allow_singular : bool, optional
Whether to allow a singular matrix. (Default: True)
Notes
-----
The arguments are similar to those of scipy.linalg.pinvh().
"""
def __init__(self, M, cond=None, rcond=None, lower=True,
check_finite=True, allow_singular=True):
# Compute the symmetric eigendecomposition.
# Note that eigh takes care of array conversion, chkfinite,
# and assertion that the matrix is square.
s, u = scipy.linalg.eigh(M, lower=lower, check_finite=check_finite)
eps = _eigvalsh_to_eps(s, cond, rcond)
if np.min(s) < -eps:
raise ValueError('the input matrix must be positive semidefinite')
d = s[s > eps]
if len(d) < len(s) and not allow_singular:
raise np.linalg.LinAlgError('singular matrix')
s_pinv = _pinv_1d(s, eps)
U = np.multiply(u, np.sqrt(s_pinv))
# Initialize the eagerly precomputed attributes.
self.rank = len(d)
self.U = U
self.log_pdet = np.sum(np.log(d))
# Initialize an attribute to be lazily computed.
self._pinv = None
@property
def pinv(self):
if self._pinv is None:
self._pinv = np.dot(self.U, self.U.T)
return self._pinv
class multi_rv_generic(object):
"""
Class which encapsulates common functionality between all multivariate
distributions.
"""
def __init__(self, seed=None):
super(multi_rv_generic, self).__init__()
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 _get_random_state(self, random_state):
if random_state is not None:
return check_random_state(random_state)
else:
return self._random_state
class multi_rv_frozen(object):
"""
Class which encapsulates common functionality between all frozen
multivariate distributions.
"""
@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)
_mvn_doc_default_callparams = """\
mean : array_like, optional
Mean of the distribution (default zero)
cov : array_like, optional
Covariance matrix of the distribution (default one)
allow_singular : bool, optional
Whether to allow a singular covariance matrix. (Default: False)
"""
_mvn_doc_callparams_note = \
"""Setting the parameter `mean` to `None` is equivalent to having `mean`
be the zero-vector. The parameter `cov` can be a scalar, in which case
the covariance matrix is the identity times that value, a vector of
diagonal entries for the covariance matrix, or a two-dimensional
array_like.
"""
_mvn_doc_frozen_callparams = ""
_mvn_doc_frozen_callparams_note = \
"""See class definition for a detailed description of parameters."""
mvn_docdict_params = {
'_mvn_doc_default_callparams': _mvn_doc_default_callparams,
'_mvn_doc_callparams_note': _mvn_doc_callparams_note,
'_doc_random_state': _doc_random_state
}
mvn_docdict_noparams = {
'_mvn_doc_default_callparams': _mvn_doc_frozen_callparams,
'_mvn_doc_callparams_note': _mvn_doc_frozen_callparams_note,
'_doc_random_state': _doc_random_state
}
class multivariate_normal_gen(multi_rv_generic):
r"""
A multivariate normal random variable.
The `mean` keyword specifies the mean. The `cov` keyword specifies the
covariance matrix.
Methods
-------
``pdf(x, mean=None, cov=1, allow_singular=False)``
Probability density function.
``logpdf(x, mean=None, cov=1, allow_singular=False)``
Log of the probability density function.
``cdf(x, mean=None, cov=1, allow_singular=False, maxpts=1000000*dim, abseps=1e-5, releps=1e-5)``
Cumulative distribution function.
``logcdf(x, mean=None, cov=1, allow_singular=False, maxpts=1000000*dim, abseps=1e-5, releps=1e-5)``
Log of the cumulative distribution function.
``rvs(mean=None, cov=1, size=1, random_state=None)``
Draw random samples from a multivariate normal distribution.
``entropy()``
Compute the differential entropy of the multivariate normal.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_mvn_doc_default_callparams)s
%(_doc_random_state)s
Alternatively, the object may be called (as a function) to fix the mean
and covariance parameters, returning a "frozen" multivariate normal
random variable:
rv = multivariate_normal(mean=None, cov=1, allow_singular=False)
- Frozen object with the same methods but holding the given
mean and covariance fixed.
Notes
-----
%(_mvn_doc_callparams_note)s
The covariance matrix `cov` must be a (symmetric) positive
semi-definite matrix. The determinant and inverse of `cov` are computed
as the pseudo-determinant and pseudo-inverse, respectively, so
that `cov` does not need to have full rank.
The probability density function for `multivariate_normal` is
.. math::
f(x) = \frac{1}{\sqrt{(2 \pi)^k \det \Sigma}}
\exp\left( -\frac{1}{2} (x - \mu)^T \Sigma^{-1} (x - \mu) \right),
where :math:`\mu` is the mean, :math:`\Sigma` the covariance matrix,
and :math:`k` is the dimension of the space where :math:`x` takes values.
.. versionadded:: 0.14.0
Examples
--------
>>> import matplotlib.pyplot as plt
>>> from scipy.stats import multivariate_normal
>>> x = np.linspace(0, 5, 10, endpoint=False)
>>> y = multivariate_normal.pdf(x, mean=2.5, cov=0.5); y
array([ 0.00108914, 0.01033349, 0.05946514, 0.20755375, 0.43939129,
0.56418958, 0.43939129, 0.20755375, 0.05946514, 0.01033349])
>>> fig1 = plt.figure()
>>> ax = fig1.add_subplot(111)
>>> ax.plot(x, y)
The input quantiles can be any shape of array, as long as the last
axis labels the components. This allows us for instance to
display the frozen pdf for a non-isotropic random variable in 2D as
follows:
>>> x, y = np.mgrid[-1:1:.01, -1:1:.01]
>>> pos = np.dstack((x, y))
>>> rv = multivariate_normal([0.5, -0.2], [[2.0, 0.3], [0.3, 0.5]])
>>> fig2 = plt.figure()
>>> ax2 = fig2.add_subplot(111)
>>> ax2.contourf(x, y, rv.pdf(pos))
"""
def __init__(self, seed=None):
super(multivariate_normal_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__, mvn_docdict_params)
def __call__(self, mean=None, cov=1, allow_singular=False, seed=None):
"""
Create a frozen multivariate normal distribution.
See `multivariate_normal_frozen` for more information.
"""
return multivariate_normal_frozen(mean, cov,
allow_singular=allow_singular,
seed=seed)
def _process_parameters(self, dim, mean, cov):
"""
Infer dimensionality from mean or covariance matrix, ensure that
mean and covariance are full vector resp. matrix.
"""
# Try to infer dimensionality
if dim is None:
if mean is None:
if cov is None:
dim = 1
else:
cov = np.asarray(cov, dtype=float)
if cov.ndim < 2:
dim = 1
else:
dim = cov.shape[0]
else:
mean = np.asarray(mean, dtype=float)
dim = mean.size
else:
if not np.isscalar(dim):
raise ValueError("Dimension of random variable must be "
"a scalar.")
# Check input sizes and return full arrays for mean and cov if
# necessary
if mean is None:
mean = np.zeros(dim)
mean = np.asarray(mean, dtype=float)
if cov is None:
cov = 1.0
cov = np.asarray(cov, dtype=float)
if dim == 1:
mean.shape = (1,)
cov.shape = (1, 1)
if mean.ndim != 1 or mean.shape[0] != dim:
raise ValueError("Array 'mean' must be a vector of length %d." %
dim)
if cov.ndim == 0:
cov = cov * np.eye(dim)
elif cov.ndim == 1:
cov = np.diag(cov)
elif cov.ndim == 2 and cov.shape != (dim, dim):
rows, cols = cov.shape
if rows != cols:
msg = ("Array 'cov' must be square if it is two dimensional,"
" but cov.shape = %s." % str(cov.shape))
else:
msg = ("Dimension mismatch: array 'cov' is of shape %s,"
" but 'mean' is a vector of length %d.")
msg = msg % (str(cov.shape), len(mean))
raise ValueError(msg)
elif cov.ndim > 2:
raise ValueError("Array 'cov' must be at most two-dimensional,"
" but cov.ndim = %d" % cov.ndim)
return dim, mean, cov
def _process_quantiles(self, x, dim):
"""
Adjust quantiles array so that last axis labels the components of
each data point.
"""
x = np.asarray(x, dtype=float)
if x.ndim == 0:
x = x[np.newaxis]
elif x.ndim == 1:
if dim == 1:
x = x[:, np.newaxis]
else:
x = x[np.newaxis, :]
return x
def _logpdf(self, x, mean, prec_U, log_det_cov, rank):
"""
Parameters
----------
x : ndarray
Points at which to evaluate the log of the probability
density function
mean : ndarray
Mean of the distribution
prec_U : ndarray
A decomposition such that np.dot(prec_U, prec_U.T)
is the precision matrix, i.e. inverse of the covariance matrix.
log_det_cov : float
Logarithm of the determinant of the covariance matrix
rank : int
Rank of the covariance matrix.
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'logpdf' instead.
"""
dev = x - mean
maha = np.sum(np.square(np.dot(dev, prec_U)), axis=-1)
return -0.5 * (rank * _LOG_2PI + log_det_cov + maha)
def logpdf(self, x, mean=None, cov=1, allow_singular=False):
"""
Log of the multivariate normal probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_mvn_doc_default_callparams)s
Returns
-------
pdf : ndarray or scalar
Log of the probability density function evaluated at `x`
Notes
-----
%(_mvn_doc_callparams_note)s
"""
dim, mean, cov = self._process_parameters(None, mean, cov)
x = self._process_quantiles(x, dim)
psd = _PSD(cov, allow_singular=allow_singular)
out = self._logpdf(x, mean, psd.U, psd.log_pdet, psd.rank)
return _squeeze_output(out)
def pdf(self, x, mean=None, cov=1, allow_singular=False):
"""
Multivariate normal probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_mvn_doc_default_callparams)s
Returns
-------
pdf : ndarray or scalar
Probability density function evaluated at `x`
Notes
-----
%(_mvn_doc_callparams_note)s
"""
dim, mean, cov = self._process_parameters(None, mean, cov)
x = self._process_quantiles(x, dim)
psd = _PSD(cov, allow_singular=allow_singular)
out = np.exp(self._logpdf(x, mean, psd.U, psd.log_pdet, psd.rank))
return _squeeze_output(out)
def _cdf(self, x, mean, cov, maxpts, abseps, releps):
"""
Parameters
----------
x : ndarray
Points at which to evaluate the cumulative distribution function.
mean : ndarray
Mean of the distribution
cov : array_like
Covariance matrix of the distribution
maxpts: integer
The maximum number of points to use for integration
abseps: float
Absolute error tolerance
releps: float
Relative error tolerance
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'cdf' instead.
.. versionadded:: 1.0.0
"""
lower = np.full(mean.shape, -np.inf)
# mvnun expects 1-d arguments, so process points sequentially
func1d = lambda x_slice: mvn.mvnun(lower, x_slice, mean, cov,
maxpts, abseps, releps)[0]
out = np.apply_along_axis(func1d, -1, x)
return _squeeze_output(out)
def logcdf(self, x, mean=None, cov=1, allow_singular=False, maxpts=None,
abseps=1e-5, releps=1e-5):
"""
Log of the multivariate normal cumulative distribution function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_mvn_doc_default_callparams)s
maxpts: integer, optional
The maximum number of points to use for integration
(default `1000000*dim`)
abseps: float, optional
Absolute error tolerance (default 1e-5)
releps: float, optional
Relative error tolerance (default 1e-5)
Returns
-------
cdf : ndarray or scalar
Log of the cumulative distribution function evaluated at `x`
Notes
-----
%(_mvn_doc_callparams_note)s
.. versionadded:: 1.0.0
"""
dim, mean, cov = self._process_parameters(None, mean, cov)
x = self._process_quantiles(x, dim)
# Use _PSD to check covariance matrix
_PSD(cov, allow_singular=allow_singular)
if not maxpts:
maxpts = 1000000 * dim
out = np.log(self._cdf(x, mean, cov, maxpts, abseps, releps))
return out
def cdf(self, x, mean=None, cov=1, allow_singular=False, maxpts=None,
abseps=1e-5, releps=1e-5):
"""
Multivariate normal cumulative distribution function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_mvn_doc_default_callparams)s
maxpts: integer, optional
The maximum number of points to use for integration
(default `1000000*dim`)
abseps: float, optional
Absolute error tolerance (default 1e-5)
releps: float, optional
Relative error tolerance (default 1e-5)
Returns
-------
cdf : ndarray or scalar
Cumulative distribution function evaluated at `x`
Notes
-----
%(_mvn_doc_callparams_note)s
.. versionadded:: 1.0.0
"""
dim, mean, cov = self._process_parameters(None, mean, cov)
x = self._process_quantiles(x, dim)
# Use _PSD to check covariance matrix
_PSD(cov, allow_singular=allow_singular)
if not maxpts:
maxpts = 1000000 * dim
out = self._cdf(x, mean, cov, maxpts, abseps, releps)
return out
def rvs(self, mean=None, cov=1, size=1, random_state=None):
"""
Draw random samples from a multivariate normal distribution.
Parameters
----------
%(_mvn_doc_default_callparams)s
size : integer, optional
Number of samples to draw (default 1).
%(_doc_random_state)s
Returns
-------
rvs : ndarray or scalar
Random variates of size (`size`, `N`), where `N` is the
dimension of the random variable.
Notes
-----
%(_mvn_doc_callparams_note)s
"""
dim, mean, cov = self._process_parameters(None, mean, cov)
random_state = self._get_random_state(random_state)
out = random_state.multivariate_normal(mean, cov, size)
return _squeeze_output(out)
def entropy(self, mean=None, cov=1):
"""
Compute the differential entropy of the multivariate normal.
Parameters
----------
%(_mvn_doc_default_callparams)s
Returns
-------
h : scalar
Entropy of the multivariate normal distribution
Notes
-----
%(_mvn_doc_callparams_note)s
"""
dim, mean, cov = self._process_parameters(None, mean, cov)
_, logdet = np.linalg.slogdet(2 * np.pi * np.e * cov)
return 0.5 * logdet
multivariate_normal = multivariate_normal_gen()
class multivariate_normal_frozen(multi_rv_frozen):
def __init__(self, mean=None, cov=1, allow_singular=False, seed=None,
maxpts=None, abseps=1e-5, releps=1e-5):
"""
Create a frozen multivariate normal distribution.
Parameters
----------
mean : array_like, optional
Mean of the distribution (default zero)
cov : array_like, optional
Covariance matrix of the distribution (default one)
allow_singular : bool, optional
If this flag is True then tolerate a singular
covariance matrix (default False).
seed : None or int or np.random.RandomState instance, optional
This parameter defines the RandomState object to use for drawing
random variates.
If None (or np.random), the global np.random state is used.
If integer, it is used to seed the local RandomState instance
Default is None.
maxpts: integer, optional
The maximum number of points to use for integration of the
cumulative distribution function (default `1000000*dim`)
abseps: float, optional
Absolute error tolerance for the cumulative distribution function
(default 1e-5)
releps: float, optional
Relative error tolerance for the cumulative distribution function
(default 1e-5)
Examples
--------
When called with the default parameters, this will create a 1D random
variable with mean 0 and covariance 1:
>>> from scipy.stats import multivariate_normal
>>> r = multivariate_normal()
>>> r.mean
array([ 0.])
>>> r.cov
array([[1.]])
"""
self._dist = multivariate_normal_gen(seed)
self.dim, self.mean, self.cov = self._dist._process_parameters(
None, mean, cov)
self.cov_info = _PSD(self.cov, allow_singular=allow_singular)
if not maxpts:
maxpts = 1000000 * self.dim
self.maxpts = maxpts
self.abseps = abseps
self.releps = releps
def logpdf(self, x):
x = self._dist._process_quantiles(x, self.dim)
out = self._dist._logpdf(x, self.mean, self.cov_info.U,
self.cov_info.log_pdet, self.cov_info.rank)
return _squeeze_output(out)
def pdf(self, x):
return np.exp(self.logpdf(x))
def logcdf(self, x):
return np.log(self.cdf(x))
def cdf(self, x):
x = self._dist._process_quantiles(x, self.dim)
out = self._dist._cdf(x, self.mean, self.cov, self.maxpts, self.abseps,
self.releps)
return _squeeze_output(out)
def rvs(self, size=1, random_state=None):
return self._dist.rvs(self.mean, self.cov, size, random_state)
def entropy(self):
"""
Computes the differential entropy of the multivariate normal.
Returns
-------
h : scalar
Entropy of the multivariate normal distribution
"""
log_pdet = self.cov_info.log_pdet
rank = self.cov_info.rank
return 0.5 * (rank * (_LOG_2PI + 1) + log_pdet)
# Set frozen generator docstrings from corresponding docstrings in
# multivariate_normal_gen and fill in default strings in class docstrings
for name in ['logpdf', 'pdf', 'logcdf', 'cdf', 'rvs']:
method = multivariate_normal_gen.__dict__[name]
method_frozen = multivariate_normal_frozen.__dict__[name]
method_frozen.__doc__ = doccer.docformat(method.__doc__,
mvn_docdict_noparams)
method.__doc__ = doccer.docformat(method.__doc__, mvn_docdict_params)
_matnorm_doc_default_callparams = """\
mean : array_like, optional
Mean of the distribution (default: `None`)
rowcov : array_like, optional
Among-row covariance matrix of the distribution (default: `1`)
colcov : array_like, optional
Among-column covariance matrix of the distribution (default: `1`)
"""
_matnorm_doc_callparams_note = \
"""If `mean` is set to `None` then a matrix of zeros is used for the mean.
The dimensions of this matrix are inferred from the shape of `rowcov` and
`colcov`, if these are provided, or set to `1` if ambiguous.
`rowcov` and `colcov` can be two-dimensional array_likes specifying the
covariance matrices directly. Alternatively, a one-dimensional array will
be be interpreted as the entries of a diagonal matrix, and a scalar or
zero-dimensional array will be interpreted as this value times the
identity matrix.
"""
_matnorm_doc_frozen_callparams = ""
_matnorm_doc_frozen_callparams_note = \
"""See class definition for a detailed description of parameters."""
matnorm_docdict_params = {
'_matnorm_doc_default_callparams': _matnorm_doc_default_callparams,
'_matnorm_doc_callparams_note': _matnorm_doc_callparams_note,
'_doc_random_state': _doc_random_state
}
matnorm_docdict_noparams = {
'_matnorm_doc_default_callparams': _matnorm_doc_frozen_callparams,
'_matnorm_doc_callparams_note': _matnorm_doc_frozen_callparams_note,
'_doc_random_state': _doc_random_state
}
class matrix_normal_gen(multi_rv_generic):
r"""
A matrix normal random variable.
The `mean` keyword specifies the mean. The `rowcov` keyword specifies the
among-row covariance matrix. The 'colcov' keyword specifies the
among-column covariance matrix.
Methods
-------
``pdf(X, mean=None, rowcov=1, colcov=1)``
Probability density function.
``logpdf(X, mean=None, rowcov=1, colcov=1)``
Log of the probability density function.
``rvs(mean=None, rowcov=1, colcov=1, size=1, random_state=None)``
Draw random samples.
Parameters
----------
X : array_like
Quantiles, with the last two axes of `X` denoting the components.
%(_matnorm_doc_default_callparams)s
%(_doc_random_state)s
Alternatively, the object may be called (as a function) to fix the mean
and covariance parameters, returning a "frozen" matrix normal
random variable:
rv = matrix_normal(mean=None, rowcov=1, colcov=1)
- Frozen object with the same methods but holding the given
mean and covariance fixed.
Notes
-----
%(_matnorm_doc_callparams_note)s
The covariance matrices specified by `rowcov` and `colcov` must be
(symmetric) positive definite. If the samples in `X` are
:math:`m \times n`, then `rowcov` must be :math:`m \times m` and
`colcov` must be :math:`n \times n`. `mean` must be the same shape as `X`.
The probability density function for `matrix_normal` is
.. math::
f(X) = (2 \pi)^{-\frac{mn}{2}}|U|^{-\frac{n}{2}} |V|^{-\frac{m}{2}}
\exp\left( -\frac{1}{2} \mathrm{Tr}\left[ U^{-1} (X-M) V^{-1}
(X-M)^T \right] \right),
where :math:`M` is the mean, :math:`U` the among-row covariance matrix,
:math:`V` the among-column covariance matrix.
The `allow_singular` behaviour of the `multivariate_normal`
distribution is not currently supported. Covariance matrices must be
full rank.
The `matrix_normal` distribution is closely related to the
`multivariate_normal` distribution. Specifically, :math:`\mathrm{Vec}(X)`
(the vector formed by concatenating the columns of :math:`X`) has a
multivariate normal distribution with mean :math:`\mathrm{Vec}(M)`
and covariance :math:`V \otimes U` (where :math:`\otimes` is the Kronecker
product). Sampling and pdf evaluation are
:math:`\mathcal{O}(m^3 + n^3 + m^2 n + m n^2)` for the matrix normal, but
:math:`\mathcal{O}(m^3 n^3)` for the equivalent multivariate normal,
making this equivalent form algorithmically inefficient.
.. versionadded:: 0.17.0
Examples
--------
>>> from scipy.stats import matrix_normal
>>> M = np.arange(6).reshape(3,2); M
array([[0, 1],
[2, 3],
[4, 5]])
>>> U = np.diag([1,2,3]); U
array([[1, 0, 0],
[0, 2, 0],
[0, 0, 3]])
>>> V = 0.3*np.identity(2); V
array([[ 0.3, 0. ],
[ 0. , 0.3]])
>>> X = M + 0.1; X
array([[ 0.1, 1.1],
[ 2.1, 3.1],
[ 4.1, 5.1]])
>>> matrix_normal.pdf(X, mean=M, rowcov=U, colcov=V)
0.023410202050005054
>>> # Equivalent multivariate normal
>>> from scipy.stats import multivariate_normal
>>> vectorised_X = X.T.flatten()
>>> equiv_mean = M.T.flatten()
>>> equiv_cov = np.kron(V,U)
>>> multivariate_normal.pdf(vectorised_X, mean=equiv_mean, cov=equiv_cov)
0.023410202050005054
"""
def __init__(self, seed=None):
super(matrix_normal_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__, matnorm_docdict_params)
def __call__(self, mean=None, rowcov=1, colcov=1, seed=None):
"""
Create a frozen matrix normal distribution.
See `matrix_normal_frozen` for more information.
"""
return matrix_normal_frozen(mean, rowcov, colcov, seed=seed)
def _process_parameters(self, mean, rowcov, colcov):
"""
Infer dimensionality from mean or covariance matrices. Handle
defaults. Ensure compatible dimensions.
"""
# Process mean
if mean is not None:
mean = np.asarray(mean, dtype=float)
meanshape = mean.shape
if len(meanshape) != 2:
raise ValueError("Array `mean` must be two dimensional.")
if np.any(meanshape == 0):
raise ValueError("Array `mean` has invalid shape.")
# Process among-row covariance
rowcov = np.asarray(rowcov, dtype=float)
if rowcov.ndim == 0:
if mean is not None:
rowcov = rowcov * np.identity(meanshape[0])
else:
rowcov = rowcov * np.identity(1)
elif rowcov.ndim == 1:
rowcov = np.diag(rowcov)
rowshape = rowcov.shape
if len(rowshape) != 2:
raise ValueError("`rowcov` must be a scalar or a 2D array.")
if rowshape[0] != rowshape[1]:
raise ValueError("Array `rowcov` must be square.")
if rowshape[0] == 0:
raise ValueError("Array `rowcov` has invalid shape.")
numrows = rowshape[0]
# Process among-column covariance
colcov = np.asarray(colcov, dtype=float)
if colcov.ndim == 0:
if mean is not None:
colcov = colcov * np.identity(meanshape[1])
else:
colcov = colcov * np.identity(1)
elif colcov.ndim == 1:
colcov = np.diag(colcov)
colshape = colcov.shape
if len(colshape) != 2:
raise ValueError("`colcov` must be a scalar or a 2D array.")
if colshape[0] != colshape[1]:
raise ValueError("Array `colcov` must be square.")
if colshape[0] == 0:
raise ValueError("Array `colcov` has invalid shape.")
numcols = colshape[0]
# Ensure mean and covariances compatible
if mean is not None:
if meanshape[0] != numrows:
raise ValueError("Arrays `mean` and `rowcov` must have the "
"same number of rows.")
if meanshape[1] != numcols:
raise ValueError("Arrays `mean` and `colcov` must have the "
"same number of columns.")
else:
mean = np.zeros((numrows, numcols))
dims = (numrows, numcols)
return dims, mean, rowcov, colcov
def _process_quantiles(self, X, dims):
"""
Adjust quantiles array so that last two axes labels the components of
each data point.
"""
X = np.asarray(X, dtype=float)
if X.ndim == 2:
X = X[np.newaxis, :]
if X.shape[-2:] != dims:
raise ValueError("The shape of array `X` is not compatible "
"with the distribution parameters.")
return X
def _logpdf(self, dims, X, mean, row_prec_rt, log_det_rowcov,
col_prec_rt, log_det_colcov):
"""
Parameters
----------
dims : tuple
Dimensions of the matrix variates
X : ndarray
Points at which to evaluate the log of the probability
density function
mean : ndarray
Mean of the distribution
row_prec_rt : ndarray
A decomposition such that np.dot(row_prec_rt, row_prec_rt.T)
is the inverse of the among-row covariance matrix
log_det_rowcov : float
Logarithm of the determinant of the among-row covariance matrix
col_prec_rt : ndarray
A decomposition such that np.dot(col_prec_rt, col_prec_rt.T)
is the inverse of the among-column covariance matrix
log_det_colcov : float
Logarithm of the determinant of the among-column covariance matrix
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'logpdf' instead.
"""
numrows, numcols = dims
roll_dev = np.rollaxis(X-mean, axis=-1, start=0)
scale_dev = np.tensordot(col_prec_rt.T,
np.dot(roll_dev, row_prec_rt), 1)
maha = np.sum(np.sum(np.square(scale_dev), axis=-1), axis=0)
return -0.5 * (numrows*numcols*_LOG_2PI + numcols*log_det_rowcov
+ numrows*log_det_colcov + maha)
def logpdf(self, X, mean=None, rowcov=1, colcov=1):
"""
Log of the matrix normal probability density function.
Parameters
----------
X : array_like
Quantiles, with the last two axes of `X` denoting the components.
%(_matnorm_doc_default_callparams)s
Returns
-------
logpdf : ndarray
Log of the probability density function evaluated at `X`
Notes
-----
%(_matnorm_doc_callparams_note)s
"""
dims, mean, rowcov, colcov = self._process_parameters(mean, rowcov,
colcov)
X = self._process_quantiles(X, dims)
rowpsd = _PSD(rowcov, allow_singular=False)
colpsd = _PSD(colcov, allow_singular=False)
out = self._logpdf(dims, X, mean, rowpsd.U, rowpsd.log_pdet, colpsd.U,
colpsd.log_pdet)
return _squeeze_output(out)
def pdf(self, X, mean=None, rowcov=1, colcov=1):
"""
Matrix normal probability density function.
Parameters
----------
X : array_like
Quantiles, with the last two axes of `X` denoting the components.
%(_matnorm_doc_default_callparams)s
Returns
-------
pdf : ndarray
Probability density function evaluated at `X`
Notes
-----
%(_matnorm_doc_callparams_note)s
"""
return np.exp(self.logpdf(X, mean, rowcov, colcov))
def rvs(self, mean=None, rowcov=1, colcov=1, size=1, random_state=None):
"""
Draw random samples from a matrix normal distribution.
Parameters
----------
%(_matnorm_doc_default_callparams)s
size : integer, optional
Number of samples to draw (default 1).
%(_doc_random_state)s
Returns
-------
rvs : ndarray or scalar
Random variates of size (`size`, `dims`), where `dims` is the
dimension of the random matrices.
Notes
-----
%(_matnorm_doc_callparams_note)s
"""
size = int(size)
dims, mean, rowcov, colcov = self._process_parameters(mean, rowcov,
colcov)
rowchol = scipy.linalg.cholesky(rowcov, lower=True)
colchol = scipy.linalg.cholesky(colcov, lower=True)
random_state = self._get_random_state(random_state)
std_norm = random_state.standard_normal(size=(dims[1], size, dims[0]))
roll_rvs = np.tensordot(colchol, np.dot(std_norm, rowchol.T), 1)
out = np.rollaxis(roll_rvs.T, axis=1, start=0) + mean[np.newaxis, :, :]
if size == 1:
out = out.reshape(mean.shape)
return out
matrix_normal = matrix_normal_gen()
class matrix_normal_frozen(multi_rv_frozen):
def __init__(self, mean=None, rowcov=1, colcov=1, seed=None):
"""
Create a frozen matrix normal distribution.
Parameters
----------
%(_matnorm_doc_default_callparams)s
seed : None or int or np.random.RandomState instance, optional
If int or RandomState, use it for drawing the random variates.
If None (or np.random), the global np.random state is used.
Default is None.
Examples
--------
>>> from scipy.stats import matrix_normal
>>> distn = matrix_normal(mean=np.zeros((3,3)))
>>> X = distn.rvs(); X
array([[-0.02976962, 0.93339138, -0.09663178],
[ 0.67405524, 0.28250467, -0.93308929],
[-0.31144782, 0.74535536, 1.30412916]])
>>> distn.pdf(X)
2.5160642368346784e-05
>>> distn.logpdf(X)
-10.590229595124615
"""
self._dist = matrix_normal_gen(seed)
self.dims, self.mean, self.rowcov, self.colcov = \
self._dist._process_parameters(mean, rowcov, colcov)
self.rowpsd = _PSD(self.rowcov, allow_singular=False)
self.colpsd = _PSD(self.colcov, allow_singular=False)
def logpdf(self, X):
X = self._dist._process_quantiles(X, self.dims)
out = self._dist._logpdf(self.dims, X, self.mean, self.rowpsd.U,
self.rowpsd.log_pdet, self.colpsd.U,
self.colpsd.log_pdet)
return _squeeze_output(out)
def pdf(self, X):
return np.exp(self.logpdf(X))
def rvs(self, size=1, random_state=None):
return self._dist.rvs(self.mean, self.rowcov, self.colcov, size,
random_state)
# Set frozen generator docstrings from corresponding docstrings in
# matrix_normal_gen and fill in default strings in class docstrings
for name in ['logpdf', 'pdf', 'rvs']:
method = matrix_normal_gen.__dict__[name]
method_frozen = matrix_normal_frozen.__dict__[name]
method_frozen.__doc__ = doccer.docformat(method.__doc__,
matnorm_docdict_noparams)
method.__doc__ = doccer.docformat(method.__doc__, matnorm_docdict_params)
_dirichlet_doc_default_callparams = """\
alpha : array_like
The concentration parameters. The number of entries determines the
dimensionality of the distribution.
"""
_dirichlet_doc_frozen_callparams = ""
_dirichlet_doc_frozen_callparams_note = \
"""See class definition for a detailed description of parameters."""
dirichlet_docdict_params = {
'_dirichlet_doc_default_callparams': _dirichlet_doc_default_callparams,
'_doc_random_state': _doc_random_state
}
dirichlet_docdict_noparams = {
'_dirichlet_doc_default_callparams': _dirichlet_doc_frozen_callparams,
'_doc_random_state': _doc_random_state
}
def _dirichlet_check_parameters(alpha):
alpha = np.asarray(alpha)
if np.min(alpha) <= 0:
raise ValueError("All parameters must be greater than 0")
elif alpha.ndim != 1:
raise ValueError("Parameter vector 'a' must be one dimensional, "
"but a.shape = %s." % (alpha.shape, ))
return alpha
def _dirichlet_check_input(alpha, x):
x = np.asarray(x)
if x.shape[0] + 1 != alpha.shape[0] and x.shape[0] != alpha.shape[0]:
raise ValueError("Vector 'x' must have either the same number "
"of entries as, or one entry fewer than, "
"parameter vector 'a', but alpha.shape = %s "
"and x.shape = %s." % (alpha.shape, x.shape))
if x.shape[0] != alpha.shape[0]:
xk = np.array([1 - np.sum(x, 0)])
if xk.ndim == 1:
x = np.append(x, xk)
elif xk.ndim == 2:
x = np.vstack((x, xk))
else:
raise ValueError("The input must be one dimensional or a two "
"dimensional matrix containing the entries.")
if np.min(x) < 0:
raise ValueError("Each entry in 'x' must be greater than or equal "
"to zero.")
if np.max(x) > 1:
raise ValueError("Each entry in 'x' must be smaller or equal one.")
# Check x_i > 0 or alpha_i > 1
xeq0 = (x == 0)
alphalt1 = (alpha < 1)
if x.shape != alpha.shape:
alphalt1 = np.repeat(alphalt1, x.shape[-1], axis=-1).reshape(x.shape)
chk = np.logical_and(xeq0, alphalt1)
if np.sum(chk):
raise ValueError("Each entry in 'x' must be greater than zero if its "
"alpha is less than one.")
if (np.abs(np.sum(x, 0) - 1.0) > 10e-10).any():
raise ValueError("The input vector 'x' must lie within the normal "
"simplex. but np.sum(x, 0) = %s." % np.sum(x, 0))
return x
def _lnB(alpha):
r"""
Internal helper function to compute the log of the useful quotient
.. math::
B(\alpha) = \frac{\prod_{i=1}{K}\Gamma(\alpha_i)}
{\Gamma\left(\sum_{i=1}^{K} \alpha_i \right)}
Parameters
----------
%(_dirichlet_doc_default_callparams)s
Returns
-------
B : scalar
Helper quotient, internal use only
"""
return np.sum(gammaln(alpha)) - gammaln(np.sum(alpha))
class dirichlet_gen(multi_rv_generic):
r"""
A Dirichlet random variable.
The `alpha` keyword specifies the concentration parameters of the
distribution.
.. versionadded:: 0.15.0
Methods
-------
``pdf(x, alpha)``
Probability density function.
``logpdf(x, alpha)``
Log of the probability density function.
``rvs(alpha, size=1, random_state=None)``
Draw random samples from a Dirichlet distribution.
``mean(alpha)``
The mean of the Dirichlet distribution
``var(alpha)``
The variance of the Dirichlet distribution
``entropy(alpha)``
Compute the differential entropy of the Dirichlet distribution.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_dirichlet_doc_default_callparams)s
%(_doc_random_state)s
Alternatively, the object may be called (as a function) to fix
concentration parameters, returning a "frozen" Dirichlet
random variable:
rv = dirichlet(alpha)
- Frozen object with the same methods but holding the given
concentration parameters fixed.
Notes
-----
Each :math:`\alpha` entry must be positive. The distribution has only
support on the simplex defined by
.. math::
\sum_{i=1}^{K} x_i \le 1
The probability density function for `dirichlet` is
.. math::
f(x) = \frac{1}{\mathrm{B}(\boldsymbol\alpha)} \prod_{i=1}^K x_i^{\alpha_i - 1}
where
.. math::
\mathrm{B}(\boldsymbol\alpha) = \frac{\prod_{i=1}^K \Gamma(\alpha_i)}
{\Gamma\bigl(\sum_{i=1}^K \alpha_i\bigr)}
and :math:`\boldsymbol\alpha=(\alpha_1,\ldots,\alpha_K)`, the
concentration parameters and :math:`K` is the dimension of the space
where :math:`x` takes values.
Note that the dirichlet interface is somewhat inconsistent.
The array returned by the rvs function is transposed
with respect to the format expected by the pdf and logpdf.
Examples
--------
>>> from scipy.stats import dirichlet
Generate a dirichlet random variable
>>> quantiles = np.array([0.2, 0.2, 0.6]) # specify quantiles
>>> alpha = np.array([0.4, 5, 15]) # specify concentration parameters
>>> dirichlet.pdf(quantiles, alpha)
0.2843831684937255
The same PDF but following a log scale
>>> dirichlet.logpdf(quantiles, alpha)
-1.2574327653159187
Once we specify the dirichlet distribution
we can then calculate quantities of interest
>>> dirichlet.mean(alpha) # get the mean of the distribution
array([0.01960784, 0.24509804, 0.73529412])
>>> dirichlet.var(alpha) # get variance
array([0.00089829, 0.00864603, 0.00909517])
>>> dirichlet.entropy(alpha) # calculate the differential entropy
-4.3280162474082715
We can also return random samples from the distribution
>>> dirichlet.rvs(alpha, size=1, random_state=1)
array([[0.00766178, 0.24670518, 0.74563305]])
>>> dirichlet.rvs(alpha, size=2, random_state=2)
array([[0.01639427, 0.1292273 , 0.85437844],
[0.00156917, 0.19033695, 0.80809388]])
"""
def __init__(self, seed=None):
super(dirichlet_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__, dirichlet_docdict_params)
def __call__(self, alpha, seed=None):
return dirichlet_frozen(alpha, seed=seed)
def _logpdf(self, x, alpha):
"""
Parameters
----------
x : ndarray
Points at which to evaluate the log of the probability
density function
%(_dirichlet_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'logpdf' instead.
"""
lnB = _lnB(alpha)
return - lnB + np.sum((xlogy(alpha - 1, x.T)).T, 0)
def logpdf(self, x, alpha):
"""
Log of the Dirichlet probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_dirichlet_doc_default_callparams)s
Returns
-------
pdf : ndarray or scalar
Log of the probability density function evaluated at `x`.
"""
alpha = _dirichlet_check_parameters(alpha)
x = _dirichlet_check_input(alpha, x)
out = self._logpdf(x, alpha)
return _squeeze_output(out)
def pdf(self, x, alpha):
"""
The Dirichlet probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_dirichlet_doc_default_callparams)s
Returns
-------
pdf : ndarray or scalar
The probability density function evaluated at `x`.
"""
alpha = _dirichlet_check_parameters(alpha)
x = _dirichlet_check_input(alpha, x)
out = np.exp(self._logpdf(x, alpha))
return _squeeze_output(out)
def mean(self, alpha):
"""
Compute the mean of the dirichlet distribution.
Parameters
----------
%(_dirichlet_doc_default_callparams)s
Returns
-------
mu : ndarray or scalar
Mean of the Dirichlet distribution.
"""
alpha = _dirichlet_check_parameters(alpha)
out = alpha / (np.sum(alpha))
return _squeeze_output(out)
def var(self, alpha):
"""
Compute the variance of the dirichlet distribution.
Parameters
----------
%(_dirichlet_doc_default_callparams)s
Returns
-------
v : ndarray or scalar
Variance of the Dirichlet distribution.
"""
alpha = _dirichlet_check_parameters(alpha)
alpha0 = np.sum(alpha)
out = (alpha * (alpha0 - alpha)) / ((alpha0 * alpha0) * (alpha0 + 1))
return _squeeze_output(out)
def entropy(self, alpha):
"""
Compute the differential entropy of the dirichlet distribution.
Parameters
----------
%(_dirichlet_doc_default_callparams)s
Returns
-------
h : scalar
Entropy of the Dirichlet distribution
"""
alpha = _dirichlet_check_parameters(alpha)
alpha0 = np.sum(alpha)
lnB = _lnB(alpha)
K = alpha.shape[0]
out = lnB + (alpha0 - K) * scipy.special.psi(alpha0) - np.sum(
(alpha - 1) * scipy.special.psi(alpha))
return _squeeze_output(out)
def rvs(self, alpha, size=1, random_state=None):
"""
Draw random samples from a Dirichlet distribution.
Parameters
----------
%(_dirichlet_doc_default_callparams)s
size : int, optional
Number of samples to draw (default 1).
%(_doc_random_state)s
Returns
-------
rvs : ndarray or scalar
Random variates of size (`size`, `N`), where `N` is the
dimension of the random variable.
"""
alpha = _dirichlet_check_parameters(alpha)
random_state = self._get_random_state(random_state)
return random_state.dirichlet(alpha, size=size)
dirichlet = dirichlet_gen()
class dirichlet_frozen(multi_rv_frozen):
def __init__(self, alpha, seed=None):
self.alpha = _dirichlet_check_parameters(alpha)
self._dist = dirichlet_gen(seed)
def logpdf(self, x):
return self._dist.logpdf(x, self.alpha)
def pdf(self, x):
return self._dist.pdf(x, self.alpha)
def mean(self):
return self._dist.mean(self.alpha)
def var(self):
return self._dist.var(self.alpha)
def entropy(self):
return self._dist.entropy(self.alpha)
def rvs(self, size=1, random_state=None):
return self._dist.rvs(self.alpha, size, random_state)
# Set frozen generator docstrings from corresponding docstrings in
# multivariate_normal_gen and fill in default strings in class docstrings
for name in ['logpdf', 'pdf', 'rvs', 'mean', 'var', 'entropy']:
method = dirichlet_gen.__dict__[name]
method_frozen = dirichlet_frozen.__dict__[name]
method_frozen.__doc__ = doccer.docformat(
method.__doc__, dirichlet_docdict_noparams)
method.__doc__ = doccer.docformat(method.__doc__, dirichlet_docdict_params)
_wishart_doc_default_callparams = """\
df : int
Degrees of freedom, must be greater than or equal to dimension of the
scale matrix
scale : array_like
Symmetric positive definite scale matrix of the distribution
"""
_wishart_doc_callparams_note = ""
_wishart_doc_frozen_callparams = ""
_wishart_doc_frozen_callparams_note = \
"""See class definition for a detailed description of parameters."""
wishart_docdict_params = {
'_doc_default_callparams': _wishart_doc_default_callparams,
'_doc_callparams_note': _wishart_doc_callparams_note,
'_doc_random_state': _doc_random_state
}
wishart_docdict_noparams = {
'_doc_default_callparams': _wishart_doc_frozen_callparams,
'_doc_callparams_note': _wishart_doc_frozen_callparams_note,
'_doc_random_state': _doc_random_state
}
class wishart_gen(multi_rv_generic):
r"""
A Wishart random variable.
The `df` keyword specifies the degrees of freedom. The `scale` keyword
specifies the scale matrix, which must be symmetric and positive definite.
In this context, the scale matrix is often interpreted in terms of a
multivariate normal precision matrix (the inverse of the covariance
matrix).
Methods
-------
``pdf(x, df, scale)``
Probability density function.
``logpdf(x, df, scale)``
Log of the probability density function.
``rvs(df, scale, size=1, random_state=None)``
Draw random samples from a Wishart distribution.
``entropy()``
Compute the differential entropy of the Wishart distribution.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_doc_default_callparams)s
%(_doc_random_state)s
Alternatively, the object may be called (as a function) to fix the degrees
of freedom and scale parameters, returning a "frozen" Wishart random
variable:
rv = wishart(df=1, scale=1)
- Frozen object with the same methods but holding the given
degrees of freedom and scale fixed.
See Also
--------
invwishart, chi2
Notes
-----
%(_doc_callparams_note)s
The scale matrix `scale` must be a symmetric positive definite
matrix. Singular matrices, including the symmetric positive semi-definite
case, are not supported.
The Wishart distribution is often denoted
.. math::
W_p(\nu, \Sigma)
where :math:`\nu` is the degrees of freedom and :math:`\Sigma` is the
:math:`p \times p` scale matrix.
The probability density function for `wishart` has support over positive
definite matrices :math:`S`; if :math:`S \sim W_p(\nu, \Sigma)`, then
its PDF is given by:
.. math::
f(S) = \frac{|S|^{\frac{\nu - p - 1}{2}}}{2^{ \frac{\nu p}{2} }
|\Sigma|^\frac{\nu}{2} \Gamma_p \left ( \frac{\nu}{2} \right )}
\exp\left( -tr(\Sigma^{-1} S) / 2 \right)
If :math:`S \sim W_p(\nu, \Sigma)` (Wishart) then
:math:`S^{-1} \sim W_p^{-1}(\nu, \Sigma^{-1})` (inverse Wishart).
If the scale matrix is 1-dimensional and equal to one, then the Wishart
distribution :math:`W_1(\nu, 1)` collapses to the :math:`\chi^2(\nu)`
distribution.
.. versionadded:: 0.16.0
References
----------
.. [1] M.L. Eaton, "Multivariate Statistics: A Vector Space Approach",
Wiley, 1983.
.. [2] W.B. Smith and R.R. Hocking, "Algorithm AS 53: Wishart Variate
Generator", Applied Statistics, vol. 21, pp. 341-345, 1972.
Examples
--------
>>> import matplotlib.pyplot as plt
>>> from scipy.stats import wishart, chi2
>>> x = np.linspace(1e-5, 8, 100)
>>> w = wishart.pdf(x, df=3, scale=1); w[:5]
array([ 0.00126156, 0.10892176, 0.14793434, 0.17400548, 0.1929669 ])
>>> c = chi2.pdf(x, 3); c[:5]
array([ 0.00126156, 0.10892176, 0.14793434, 0.17400548, 0.1929669 ])
>>> plt.plot(x, w)
The input quantiles can be any shape of array, as long as the last
axis labels the components.
"""
def __init__(self, seed=None):
super(wishart_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__, wishart_docdict_params)
def __call__(self, df=None, scale=None, seed=None):
"""
Create a frozen Wishart distribution.
See `wishart_frozen` for more information.
"""
return wishart_frozen(df, scale, seed)
def _process_parameters(self, df, scale):
if scale is None:
scale = 1.0
scale = np.asarray(scale, dtype=float)
if scale.ndim == 0:
scale = scale[np.newaxis, np.newaxis]
elif scale.ndim == 1:
scale = np.diag(scale)
elif scale.ndim == 2 and not scale.shape[0] == scale.shape[1]:
raise ValueError("Array 'scale' must be square if it is two"
" dimensional, but scale.scale = %s."
% str(scale.shape))
elif scale.ndim > 2:
raise ValueError("Array 'scale' must be at most two-dimensional,"
" but scale.ndim = %d" % scale.ndim)
dim = scale.shape[0]
if df is None:
df = dim
elif not np.isscalar(df):
raise ValueError("Degrees of freedom must be a scalar.")
elif df < dim:
raise ValueError("Degrees of freedom cannot be less than dimension"
" of scale matrix, but df = %d" % df)
return dim, df, scale
def _process_quantiles(self, x, dim):
"""
Adjust quantiles array so that last axis labels the components of
each data point.
"""
x = np.asarray(x, dtype=float)
if x.ndim == 0:
x = x * np.eye(dim)[:, :, np.newaxis]
if x.ndim == 1:
if dim == 1:
x = x[np.newaxis, np.newaxis, :]
else:
x = np.diag(x)[:, :, np.newaxis]
elif x.ndim == 2:
if not x.shape[0] == x.shape[1]:
raise ValueError("Quantiles must be square if they are two"
" dimensional, but x.shape = %s."
% str(x.shape))
x = x[:, :, np.newaxis]
elif x.ndim == 3:
if not x.shape[0] == x.shape[1]:
raise ValueError("Quantiles must be square in the first two"
" dimensions if they are three dimensional"
", but x.shape = %s." % str(x.shape))
elif x.ndim > 3:
raise ValueError("Quantiles must be at most two-dimensional with"
" an additional dimension for multiple"
"components, but x.ndim = %d" % x.ndim)
# Now we have 3-dim array; should have shape [dim, dim, *]
if not x.shape[0:2] == (dim, dim):
raise ValueError('Quantiles have incompatible dimensions: should'
' be %s, got %s.' % ((dim, dim), x.shape[0:2]))
return x
def _process_size(self, size):
size = np.asarray(size)
if size.ndim == 0:
size = size[np.newaxis]
elif size.ndim > 1:
raise ValueError('Size must be an integer or tuple of integers;'
' thus must have dimension <= 1.'
' Got size.ndim = %s' % str(tuple(size)))
n = size.prod()
shape = tuple(size)
return n, shape
def _logpdf(self, x, dim, df, scale, log_det_scale, C):
"""
Parameters
----------
x : ndarray
Points at which to evaluate the log of the probability
density function
dim : int
Dimension of the scale matrix
df : int
Degrees of freedom
scale : ndarray
Scale matrix
log_det_scale : float
Logarithm of the determinant of the scale matrix
C : ndarray
Cholesky factorization of the scale matrix, lower triagular.
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'logpdf' instead.
"""
# log determinant of x
# Note: x has components along the last axis, so that x.T has
# components alone the 0-th axis. Then since det(A) = det(A'), this
# gives us a 1-dim vector of determinants
# Retrieve tr(scale^{-1} x)
log_det_x = np.zeros(x.shape[-1])
scale_inv_x = np.zeros(x.shape)
tr_scale_inv_x = np.zeros(x.shape[-1])
for i in range(x.shape[-1]):
_, log_det_x[i] = self._cholesky_logdet(x[:, :, i])
scale_inv_x[:, :, i] = scipy.linalg.cho_solve((C, True), x[:, :, i])
tr_scale_inv_x[i] = scale_inv_x[:, :, i].trace()
# Log PDF
out = ((0.5 * (df - dim - 1) * log_det_x - 0.5 * tr_scale_inv_x) -
(0.5 * df * dim * _LOG_2 + 0.5 * df * log_det_scale +
multigammaln(0.5*df, dim)))
return out
def logpdf(self, x, df, scale):
"""
Log of the Wishart probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
Each quantile must be a symmetric positive definite matrix.
%(_doc_default_callparams)s
Returns
-------
pdf : ndarray
Log of the probability density function evaluated at `x`
Notes
-----
%(_doc_callparams_note)s
"""
dim, df, scale = self._process_parameters(df, scale)
x = self._process_quantiles(x, dim)
# Cholesky decomposition of scale, get log(det(scale))
C, log_det_scale = self._cholesky_logdet(scale)
out = self._logpdf(x, dim, df, scale, log_det_scale, C)
return _squeeze_output(out)
def pdf(self, x, df, scale):
"""
Wishart probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
Each quantile must be a symmetric positive definite matrix.
%(_doc_default_callparams)s
Returns
-------
pdf : ndarray
Probability density function evaluated at `x`
Notes
-----
%(_doc_callparams_note)s
"""
return np.exp(self.logpdf(x, df, scale))
def _mean(self, dim, df, scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
%(_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'mean' instead.
"""
return df * scale
def mean(self, df, scale):
"""
Mean of the Wishart distribution
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
mean : float
The mean of the distribution
"""
dim, df, scale = self._process_parameters(df, scale)
out = self._mean(dim, df, scale)
return _squeeze_output(out)
def _mode(self, dim, df, scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
%(_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'mode' instead.
"""
if df >= dim + 1:
out = (df-dim-1) * scale
else:
out = None
return out
def mode(self, df, scale):
"""
Mode of the Wishart distribution
Only valid if the degrees of freedom are greater than the dimension of
the scale matrix.
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
mode : float or None
The Mode of the distribution
"""
dim, df, scale = self._process_parameters(df, scale)
out = self._mode(dim, df, scale)
return _squeeze_output(out) if out is not None else out
def _var(self, dim, df, scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
%(_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'var' instead.
"""
var = scale**2
diag = scale.diagonal() # 1 x dim array
var += np.outer(diag, diag)
var *= df
return var
def var(self, df, scale):
"""
Variance of the Wishart distribution
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
var : float
The variance of the distribution
"""
dim, df, scale = self._process_parameters(df, scale)
out = self._var(dim, df, scale)
return _squeeze_output(out)
def _standard_rvs(self, n, shape, dim, df, random_state):
"""
Parameters
----------
n : integer
Number of variates to generate
shape : iterable
Shape of the variates to generate
dim : int
Dimension of the scale matrix
df : int
Degrees of freedom
random_state : np.random.RandomState instance
RandomState used for drawing the random variates.
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'rvs' instead.
"""
# Random normal variates for off-diagonal elements
n_tril = dim * (dim-1) // 2
covariances = random_state.normal(
size=n*n_tril).reshape(shape+(n_tril,))
# Random chi-square variates for diagonal elements
variances = (np.r_[[random_state.chisquare(df-(i+1)+1, size=n)**0.5
for i in range(dim)]].reshape((dim,) +
shape[::-1]).T)
# Create the A matri(ces) - lower triangular
A = np.zeros(shape + (dim, dim))
# Input the covariances
size_idx = tuple([slice(None, None, None)]*len(shape))
tril_idx = np.tril_indices(dim, k=-1)
A[size_idx + tril_idx] = covariances
# Input the variances
diag_idx = np.diag_indices(dim)
A[size_idx + diag_idx] = variances
return A
def _rvs(self, n, shape, dim, df, C, random_state):
"""
Parameters
----------
n : integer
Number of variates to generate
shape : iterable
Shape of the variates to generate
dim : int
Dimension of the scale matrix
df : int
Degrees of freedom
scale : ndarray
Scale matrix
C : ndarray
Cholesky factorization of the scale matrix, lower triangular.
%(_doc_random_state)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'rvs' instead.
"""
random_state = self._get_random_state(random_state)
# Calculate the matrices A, which are actually lower triangular
# Cholesky factorizations of a matrix B such that B ~ W(df, I)
A = self._standard_rvs(n, shape, dim, df, random_state)
# Calculate SA = C A A' C', where SA ~ W(df, scale)
# Note: this is the product of a (lower) (lower) (lower)' (lower)'
# or, denoting B = AA', it is C B C' where C is the lower
# triangular Cholesky factorization of the scale matrix.
# this appears to conflict with the instructions in [1]_, which
# suggest that it should be D' B D where D is the lower
# triangular factorization of the scale matrix. However, it is
# meant to refer to the Bartlett (1933) representation of a
# Wishart random variate as L A A' L' where L is lower triangular
# so it appears that understanding D' to be upper triangular
# is either a typo in or misreading of [1]_.
for index in np.ndindex(shape):
CA = np.dot(C, A[index])
A[index] = np.dot(CA, CA.T)
return A
def rvs(self, df, scale, size=1, random_state=None):
"""
Draw random samples from a Wishart distribution.
Parameters
----------
%(_doc_default_callparams)s
size : integer or iterable of integers, optional
Number of samples to draw (default 1).
%(_doc_random_state)s
Returns
-------
rvs : ndarray
Random variates of shape (`size`) + (`dim`, `dim), where `dim` is
the dimension of the scale matrix.
Notes
-----
%(_doc_callparams_note)s
"""
n, shape = self._process_size(size)
dim, df, scale = self._process_parameters(df, scale)
# Cholesky decomposition of scale
C = scipy.linalg.cholesky(scale, lower=True)
out = self._rvs(n, shape, dim, df, C, random_state)
return _squeeze_output(out)
def _entropy(self, dim, df, log_det_scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
df : int
Degrees of freedom
log_det_scale : float
Logarithm of the determinant of the scale matrix
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'entropy' instead.
"""
return (
0.5 * (dim+1) * log_det_scale +
0.5 * dim * (dim+1) * _LOG_2 +
multigammaln(0.5*df, dim) -
0.5 * (df - dim - 1) * np.sum(
[psi(0.5*(df + 1 - (i+1))) for i in range(dim)]
) +
0.5 * df * dim
)
def entropy(self, df, scale):
"""
Compute the differential entropy of the Wishart.
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
h : scalar
Entropy of the Wishart distribution
Notes
-----
%(_doc_callparams_note)s
"""
dim, df, scale = self._process_parameters(df, scale)
_, log_det_scale = self._cholesky_logdet(scale)
return self._entropy(dim, df, log_det_scale)
def _cholesky_logdet(self, scale):
"""
Compute Cholesky decomposition and determine (log(det(scale)).
Parameters
----------
scale : ndarray
Scale matrix.
Returns
-------
c_decomp : ndarray
The Cholesky decomposition of `scale`.
logdet : scalar
The log of the determinant of `scale`.
Notes
-----
This computation of ``logdet`` is equivalent to
``np.linalg.slogdet(scale)``. It is ~2x faster though.
"""
c_decomp = scipy.linalg.cholesky(scale, lower=True)
logdet = 2 * np.sum(np.log(c_decomp.diagonal()))
return c_decomp, logdet
wishart = wishart_gen()
class wishart_frozen(multi_rv_frozen):
"""
Create a frozen Wishart distribution.
Parameters
----------
df : array_like
Degrees of freedom of the distribution
scale : array_like
Scale matrix of the distribution
seed : None or int or np.random.RandomState instance, optional
This parameter defines the RandomState object to use for drawing
random variates.
If None (or np.random), the global np.random state is used.
If integer, it is used to seed the local RandomState instance
Default is None.
"""
def __init__(self, df, scale, seed=None):
self._dist = wishart_gen(seed)
self.dim, self.df, self.scale = self._dist._process_parameters(
df, scale)
self.C, self.log_det_scale = self._dist._cholesky_logdet(self.scale)
def logpdf(self, x):
x = self._dist._process_quantiles(x, self.dim)
out = self._dist._logpdf(x, self.dim, self.df, self.scale,
self.log_det_scale, self.C)
return _squeeze_output(out)
def pdf(self, x):
return np.exp(self.logpdf(x))
def mean(self):
out = self._dist._mean(self.dim, self.df, self.scale)
return _squeeze_output(out)
def mode(self):
out = self._dist._mode(self.dim, self.df, self.scale)
return _squeeze_output(out) if out is not None else out
def var(self):
out = self._dist._var(self.dim, self.df, self.scale)
return _squeeze_output(out)
def rvs(self, size=1, random_state=None):
n, shape = self._dist._process_size(size)
out = self._dist._rvs(n, shape, self.dim, self.df,
self.C, random_state)
return _squeeze_output(out)
def entropy(self):
return self._dist._entropy(self.dim, self.df, self.log_det_scale)
# Set frozen generator docstrings from corresponding docstrings in
# Wishart and fill in default strings in class docstrings
for name in ['logpdf', 'pdf', 'mean', 'mode', 'var', 'rvs', 'entropy']:
method = wishart_gen.__dict__[name]
method_frozen = wishart_frozen.__dict__[name]
method_frozen.__doc__ = doccer.docformat(
method.__doc__, wishart_docdict_noparams)
method.__doc__ = doccer.docformat(method.__doc__, wishart_docdict_params)
def _cho_inv_batch(a, check_finite=True):
"""
Invert the matrices a_i, using a Cholesky factorization of A, where
a_i resides in the last two dimensions of a and the other indices describe
the index i.
Overwrites the data in a.
Parameters
----------
a : array
Array of matrices to invert, where the matrices themselves are stored
in the last two dimensions.
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
x : array
Array of inverses of the matrices ``a_i``.
See also
--------
scipy.linalg.cholesky : Cholesky factorization of a matrix
"""
if check_finite:
a1 = asarray_chkfinite(a)
else:
a1 = asarray(a)
if len(a1.shape) < 2 or a1.shape[-2] != a1.shape[-1]:
raise ValueError('expected square matrix in last two dimensions')
potrf, potri = get_lapack_funcs(('potrf', 'potri'), (a1,))
triu_rows, triu_cols = np.triu_indices(a.shape[-2], k=1)
for index in np.ndindex(a1.shape[:-2]):
# Cholesky decomposition
a1[index], info = potrf(a1[index], lower=True, overwrite_a=False,
clean=False)
if info > 0:
raise LinAlgError("%d-th leading minor not positive definite"
% info)
if info < 0:
raise ValueError('illegal value in %d-th argument of internal'
' potrf' % -info)
# Inversion
a1[index], info = potri(a1[index], lower=True, overwrite_c=False)
if info > 0:
raise LinAlgError("the inverse could not be computed")
if info < 0:
raise ValueError('illegal value in %d-th argument of internal'
' potrf' % -info)
# Make symmetric (dpotri only fills in the lower triangle)
a1[index][triu_rows, triu_cols] = a1[index][triu_cols, triu_rows]
return a1
class invwishart_gen(wishart_gen):
r"""
An inverse Wishart random variable.
The `df` keyword specifies the degrees of freedom. The `scale` keyword
specifies the scale matrix, which must be symmetric and positive definite.
In this context, the scale matrix is often interpreted in terms of a
multivariate normal covariance matrix.
Methods
-------
``pdf(x, df, scale)``
Probability density function.
``logpdf(x, df, scale)``
Log of the probability density function.
``rvs(df, scale, size=1, random_state=None)``
Draw random samples from an inverse Wishart distribution.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_doc_default_callparams)s
%(_doc_random_state)s
Alternatively, the object may be called (as a function) to fix the degrees
of freedom and scale parameters, returning a "frozen" inverse Wishart
random variable:
rv = invwishart(df=1, scale=1)
- Frozen object with the same methods but holding the given
degrees of freedom and scale fixed.
See Also
--------
wishart
Notes
-----
%(_doc_callparams_note)s
The scale matrix `scale` must be a symmetric positive definite
matrix. Singular matrices, including the symmetric positive semi-definite
case, are not supported.
The inverse Wishart distribution is often denoted
.. math::
W_p^{-1}(\nu, \Psi)
where :math:`\nu` is the degrees of freedom and :math:`\Psi` is the
:math:`p \times p` scale matrix.
The probability density function for `invwishart` has support over positive
definite matrices :math:`S`; if :math:`S \sim W^{-1}_p(\nu, \Sigma)`,
then its PDF is given by:
.. math::
f(S) = \frac{|\Sigma|^\frac{\nu}{2}}{2^{ \frac{\nu p}{2} }
|S|^{\frac{\nu + p + 1}{2}} \Gamma_p \left(\frac{\nu}{2} \right)}
\exp\left( -tr(\Sigma S^{-1}) / 2 \right)
If :math:`S \sim W_p^{-1}(\nu, \Psi)` (inverse Wishart) then
:math:`S^{-1} \sim W_p(\nu, \Psi^{-1})` (Wishart).
If the scale matrix is 1-dimensional and equal to one, then the inverse
Wishart distribution :math:`W_1(\nu, 1)` collapses to the
inverse Gamma distribution with parameters shape = :math:`\frac{\nu}{2}`
and scale = :math:`\frac{1}{2}`.
.. versionadded:: 0.16.0
References
----------
.. [1] M.L. Eaton, "Multivariate Statistics: A Vector Space Approach",
Wiley, 1983.
.. [2] M.C. Jones, "Generating Inverse Wishart Matrices", Communications
in Statistics - Simulation and Computation, vol. 14.2, pp.511-514,
1985.
Examples
--------
>>> import matplotlib.pyplot as plt
>>> from scipy.stats import invwishart, invgamma
>>> x = np.linspace(0.01, 1, 100)
>>> iw = invwishart.pdf(x, df=6, scale=1)
>>> iw[:3]
array([ 1.20546865e-15, 5.42497807e-06, 4.45813929e-03])
>>> ig = invgamma.pdf(x, 6/2., scale=1./2)
>>> ig[:3]
array([ 1.20546865e-15, 5.42497807e-06, 4.45813929e-03])
>>> plt.plot(x, iw)
The input quantiles can be any shape of array, as long as the last
axis labels the components.
"""
def __init__(self, seed=None):
super(invwishart_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__, wishart_docdict_params)
def __call__(self, df=None, scale=None, seed=None):
"""
Create a frozen inverse Wishart distribution.
See `invwishart_frozen` for more information.
"""
return invwishart_frozen(df, scale, seed)
def _logpdf(self, x, dim, df, scale, log_det_scale):
"""
Parameters
----------
x : ndarray
Points at which to evaluate the log of the probability
density function.
dim : int
Dimension of the scale matrix
df : int
Degrees of freedom
scale : ndarray
Scale matrix
log_det_scale : float
Logarithm of the determinant of the scale matrix
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'logpdf' instead.
"""
log_det_x = np.zeros(x.shape[-1])
x_inv = np.copy(x).T
if dim > 1:
_cho_inv_batch(x_inv) # works in-place
else:
x_inv = 1./x_inv
tr_scale_x_inv = np.zeros(x.shape[-1])
for i in range(x.shape[-1]):
C, lower = scipy.linalg.cho_factor(x[:, :, i], lower=True)
log_det_x[i] = 2 * np.sum(np.log(C.diagonal()))
tr_scale_x_inv[i] = np.dot(scale, x_inv[i]).trace()
# Log PDF
out = ((0.5 * df * log_det_scale - 0.5 * tr_scale_x_inv) -
(0.5 * df * dim * _LOG_2 + 0.5 * (df + dim + 1) * log_det_x) -
multigammaln(0.5*df, dim))
return out
def logpdf(self, x, df, scale):
"""
Log of the inverse Wishart probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
Each quantile must be a symmetric positive definite matrix.
%(_doc_default_callparams)s
Returns
-------
pdf : ndarray
Log of the probability density function evaluated at `x`
Notes
-----
%(_doc_callparams_note)s
"""
dim, df, scale = self._process_parameters(df, scale)
x = self._process_quantiles(x, dim)
_, log_det_scale = self._cholesky_logdet(scale)
out = self._logpdf(x, dim, df, scale, log_det_scale)
return _squeeze_output(out)
def pdf(self, x, df, scale):
"""
Inverse Wishart probability density function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
Each quantile must be a symmetric positive definite matrix.
%(_doc_default_callparams)s
Returns
-------
pdf : ndarray
Probability density function evaluated at `x`
Notes
-----
%(_doc_callparams_note)s
"""
return np.exp(self.logpdf(x, df, scale))
def _mean(self, dim, df, scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
%(_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'mean' instead.
"""
if df > dim + 1:
out = scale / (df - dim - 1)
else:
out = None
return out
def mean(self, df, scale):
"""
Mean of the inverse Wishart distribution
Only valid if the degrees of freedom are greater than the dimension of
the scale matrix plus one.
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
mean : float or None
The mean of the distribution
"""
dim, df, scale = self._process_parameters(df, scale)
out = self._mean(dim, df, scale)
return _squeeze_output(out) if out is not None else out
def _mode(self, dim, df, scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
%(_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'mode' instead.
"""
return scale / (df + dim + 1)
def mode(self, df, scale):
"""
Mode of the inverse Wishart distribution
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
mode : float
The Mode of the distribution
"""
dim, df, scale = self._process_parameters(df, scale)
out = self._mode(dim, df, scale)
return _squeeze_output(out)
def _var(self, dim, df, scale):
"""
Parameters
----------
dim : int
Dimension of the scale matrix
%(_doc_default_callparams)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'var' instead.
"""
if df > dim + 3:
var = (df - dim + 1) * scale**2
diag = scale.diagonal() # 1 x dim array
var += (df - dim - 1) * np.outer(diag, diag)
var /= (df - dim) * (df - dim - 1)**2 * (df - dim - 3)
else:
var = None
return var
def var(self, df, scale):
"""
Variance of the inverse Wishart distribution
Only valid if the degrees of freedom are greater than the dimension of
the scale matrix plus three.
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
var : float
The variance of the distribution
"""
dim, df, scale = self._process_parameters(df, scale)
out = self._var(dim, df, scale)
return _squeeze_output(out) if out is not None else out
def _rvs(self, n, shape, dim, df, C, random_state):
"""
Parameters
----------
n : integer
Number of variates to generate
shape : iterable
Shape of the variates to generate
dim : int
Dimension of the scale matrix
df : int
Degrees of freedom
C : ndarray
Cholesky factorization of the scale matrix, lower triagular.
%(_doc_random_state)s
Notes
-----
As this function does no argument checking, it should not be
called directly; use 'rvs' instead.
"""
random_state = self._get_random_state(random_state)
# Get random draws A such that A ~ W(df, I)
A = super(invwishart_gen, self)._standard_rvs(n, shape, dim,
df, random_state)
# Calculate SA = (CA)'^{-1} (CA)^{-1} ~ iW(df, scale)
eye = np.eye(dim)
trtrs = get_lapack_funcs(('trtrs'), (A,))
for index in np.ndindex(A.shape[:-2]):
# Calculate CA
CA = np.dot(C, A[index])
# Get (C A)^{-1} via triangular solver
if dim > 1:
CA, info = trtrs(CA, eye, lower=True)
if info > 0:
raise LinAlgError("Singular matrix.")
if info < 0:
raise ValueError('Illegal value in %d-th argument of'
' internal trtrs' % -info)
else:
CA = 1. / CA
# Get SA
A[index] = np.dot(CA.T, CA)
return A
def rvs(self, df, scale, size=1, random_state=None):
"""
Draw random samples from an inverse Wishart distribution.
Parameters
----------
%(_doc_default_callparams)s
size : integer or iterable of integers, optional
Number of samples to draw (default 1).
%(_doc_random_state)s
Returns
-------
rvs : ndarray
Random variates of shape (`size`) + (`dim`, `dim), where `dim` is
the dimension of the scale matrix.
Notes
-----
%(_doc_callparams_note)s
"""
n, shape = self._process_size(size)
dim, df, scale = self._process_parameters(df, scale)
# Invert the scale
eye = np.eye(dim)
L, lower = scipy.linalg.cho_factor(scale, lower=True)
inv_scale = scipy.linalg.cho_solve((L, lower), eye)
# Cholesky decomposition of inverted scale
C = scipy.linalg.cholesky(inv_scale, lower=True)
out = self._rvs(n, shape, dim, df, C, random_state)
return _squeeze_output(out)
def entropy(self):
# Need to find reference for inverse Wishart entropy
raise AttributeError
invwishart = invwishart_gen()
class invwishart_frozen(multi_rv_frozen):
def __init__(self, df, scale, seed=None):
"""
Create a frozen inverse Wishart distribution.
Parameters
----------
df : array_like
Degrees of freedom of the distribution
scale : array_like
Scale matrix of the distribution
seed : None or int or np.random.RandomState instance, optional
This parameter defines the RandomState object to use for drawing
random variates.
If None (or np.random), the global np.random state is used.
If integer, it is used to seed the local RandomState instance
Default is None.
"""
self._dist = invwishart_gen(seed)
self.dim, self.df, self.scale = self._dist._process_parameters(
df, scale
)
# Get the determinant via Cholesky factorization
C, lower = scipy.linalg.cho_factor(self.scale, lower=True)
self.log_det_scale = 2 * np.sum(np.log(C.diagonal()))
# Get the inverse using the Cholesky factorization
eye = np.eye(self.dim)
self.inv_scale = scipy.linalg.cho_solve((C, lower), eye)
# Get the Cholesky factorization of the inverse scale
self.C = scipy.linalg.cholesky(self.inv_scale, lower=True)
def logpdf(self, x):
x = self._dist._process_quantiles(x, self.dim)
out = self._dist._logpdf(x, self.dim, self.df, self.scale,
self.log_det_scale)
return _squeeze_output(out)
def pdf(self, x):
return np.exp(self.logpdf(x))
def mean(self):
out = self._dist._mean(self.dim, self.df, self.scale)
return _squeeze_output(out) if out is not None else out
def mode(self):
out = self._dist._mode(self.dim, self.df, self.scale)
return _squeeze_output(out)
def var(self):
out = self._dist._var(self.dim, self.df, self.scale)
return _squeeze_output(out) if out is not None else out
def rvs(self, size=1, random_state=None):
n, shape = self._dist._process_size(size)
out = self._dist._rvs(n, shape, self.dim, self.df,
self.C, random_state)
return _squeeze_output(out)
def entropy(self):
# Need to find reference for inverse Wishart entropy
raise AttributeError
# Set frozen generator docstrings from corresponding docstrings in
# inverse Wishart and fill in default strings in class docstrings
for name in ['logpdf', 'pdf', 'mean', 'mode', 'var', 'rvs']:
method = invwishart_gen.__dict__[name]
method_frozen = wishart_frozen.__dict__[name]
method_frozen.__doc__ = doccer.docformat(
method.__doc__, wishart_docdict_noparams)
method.__doc__ = doccer.docformat(method.__doc__, wishart_docdict_params)
_multinomial_doc_default_callparams = """\
n : int
Number of trials
p : array_like
Probability of a trial falling into each category; should sum to 1
"""
_multinomial_doc_callparams_note = \
"""`n` should be a positive integer. Each element of `p` should be in the
interval :math:`[0,1]` and the elements should sum to 1. If they do not sum to
1, the last element of the `p` array is not used and is replaced with the
remaining probability left over from the earlier elements.
"""
_multinomial_doc_frozen_callparams = ""
_multinomial_doc_frozen_callparams_note = \
"""See class definition for a detailed description of parameters."""
multinomial_docdict_params = {
'_doc_default_callparams': _multinomial_doc_default_callparams,
'_doc_callparams_note': _multinomial_doc_callparams_note,
'_doc_random_state': _doc_random_state
}
multinomial_docdict_noparams = {
'_doc_default_callparams': _multinomial_doc_frozen_callparams,
'_doc_callparams_note': _multinomial_doc_frozen_callparams_note,
'_doc_random_state': _doc_random_state
}
class multinomial_gen(multi_rv_generic):
r"""
A multinomial random variable.
Methods
-------
``pmf(x, n, p)``
Probability mass function.
``logpmf(x, n, p)``
Log of the probability mass function.
``rvs(n, p, size=1, random_state=None)``
Draw random samples from a multinomial distribution.
``entropy(n, p)``
Compute the entropy of the multinomial distribution.
``cov(n, p)``
Compute the covariance matrix of the multinomial distribution.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_doc_default_callparams)s
%(_doc_random_state)s
Notes
-----
%(_doc_callparams_note)s
Alternatively, the object may be called (as a function) to fix the `n` and
`p` parameters, returning a "frozen" multinomial random variable:
The probability mass function for `multinomial` is
.. math::
f(x) = \frac{n!}{x_1! \cdots x_k!} p_1^{x_1} \cdots p_k^{x_k},
supported on :math:`x=(x_1, \ldots, x_k)` where each :math:`x_i` is a
nonnegative integer and their sum is :math:`n`.
.. versionadded:: 0.19.0
Examples
--------
>>> from scipy.stats import multinomial
>>> rv = multinomial(8, [0.3, 0.2, 0.5])
>>> rv.pmf([1, 3, 4])
0.042000000000000072
The multinomial distribution for :math:`k=2` is identical to the
corresponding binomial distribution (tiny numerical differences
notwithstanding):
>>> from scipy.stats import binom
>>> multinomial.pmf([3, 4], n=7, p=[0.4, 0.6])
0.29030399999999973
>>> binom.pmf(3, 7, 0.4)
0.29030400000000012
The functions ``pmf``, ``logpmf``, ``entropy``, and ``cov`` support
broadcasting, under the convention that the vector parameters (``x`` and
``p``) are interpreted as if each row along the last axis is a single
object. For instance:
>>> multinomial.pmf([[3, 4], [3, 5]], n=[7, 8], p=[.3, .7])
array([0.2268945, 0.25412184])
Here, ``x.shape == (2, 2)``, ``n.shape == (2,)``, and ``p.shape == (2,)``,
but following the rules mentioned above they behave as if the rows
``[3, 4]`` and ``[3, 5]`` in ``x`` and ``[.3, .7]`` in ``p`` were a single
object, and as if we had ``x.shape = (2,)``, ``n.shape = (2,)``, and
``p.shape = ()``. To obtain the individual elements without broadcasting,
we would do this:
>>> multinomial.pmf([3, 4], n=7, p=[.3, .7])
0.2268945
>>> multinomial.pmf([3, 5], 8, p=[.3, .7])
0.25412184
This broadcasting also works for ``cov``, where the output objects are
square matrices of size ``p.shape[-1]``. For example:
>>> multinomial.cov([4, 5], [[.3, .7], [.4, .6]])
array([[[ 0.84, -0.84],
[-0.84, 0.84]],
[[ 1.2 , -1.2 ],
[-1.2 , 1.2 ]]])
In this example, ``n.shape == (2,)`` and ``p.shape == (2, 2)``, and
following the rules above, these broadcast as if ``p.shape == (2,)``.
Thus the result should also be of shape ``(2,)``, but since each output is
a :math:`2 \times 2` matrix, the result in fact has shape ``(2, 2, 2)``,
where ``result[0]`` is equal to ``multinomial.cov(n=4, p=[.3, .7])`` and
``result[1]`` is equal to ``multinomial.cov(n=5, p=[.4, .6])``.
See also
--------
scipy.stats.binom : The binomial distribution.
numpy.random.multinomial : Sampling from the multinomial distribution.
"""
def __init__(self, seed=None):
super(multinomial_gen, self).__init__(seed)
self.__doc__ = \
doccer.docformat(self.__doc__, multinomial_docdict_params)
def __call__(self, n, p, seed=None):
"""
Create a frozen multinomial distribution.
See `multinomial_frozen` for more information.
"""
return multinomial_frozen(n, p, seed)
def _process_parameters(self, n, p):
"""
Return: n_, p_, npcond.
n_ and p_ are arrays of the correct shape; npcond is a boolean array
flagging values out of the domain.
"""
p = np.array(p, dtype=np.float64, copy=True)
p[..., -1] = 1. - p[..., :-1].sum(axis=-1)
# true for bad p
pcond = np.any(p < 0, axis=-1)
pcond |= np.any(p > 1, axis=-1)
n = np.array(n, dtype=np.int, copy=True)
# true for bad n
ncond = n <= 0
return n, p, ncond | pcond
def _process_quantiles(self, x, n, p):
"""
Return: x_, xcond.
x_ is an int array; xcond is a boolean array flagging values out of the
domain.
"""
xx = np.asarray(x, dtype=np.int)
if xx.ndim == 0:
raise ValueError("x must be an array.")
if xx.size != 0 and not xx.shape[-1] == p.shape[-1]:
raise ValueError("Size of each quantile should be size of p: "
"received %d, but expected %d." %
(xx.shape[-1], p.shape[-1]))
# true for x out of the domain
cond = np.any(xx != x, axis=-1)
cond |= np.any(xx < 0, axis=-1)
cond = cond | (np.sum(xx, axis=-1) != n)
return xx, cond
def _checkresult(self, result, cond, bad_value):
result = np.asarray(result)
if cond.ndim != 0:
result[cond] = bad_value
elif cond:
if result.ndim == 0:
return bad_value
result[...] = bad_value
return result
def _logpmf(self, x, n, p):
return gammaln(n+1) + np.sum(xlogy(x, p) - gammaln(x+1), axis=-1)
def logpmf(self, x, n, p):
"""
Log of the Multinomial probability mass function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_doc_default_callparams)s
Returns
-------
logpmf : ndarray or scalar
Log of the probability mass function evaluated at `x`
Notes
-----
%(_doc_callparams_note)s
"""
n, p, npcond = self._process_parameters(n, p)
x, xcond = self._process_quantiles(x, n, p)
result = self._logpmf(x, n, p)
# replace values for which x was out of the domain; broadcast
# xcond to the right shape
xcond_ = xcond | np.zeros(npcond.shape, dtype=np.bool_)
result = self._checkresult(result, xcond_, np.NINF)
# replace values bad for n or p; broadcast npcond to the right shape
npcond_ = npcond | np.zeros(xcond.shape, dtype=np.bool_)
return self._checkresult(result, npcond_, np.NAN)
def pmf(self, x, n, p):
"""
Multinomial probability mass function.
Parameters
----------
x : array_like
Quantiles, with the last axis of `x` denoting the components.
%(_doc_default_callparams)s
Returns
-------
pmf : ndarray or scalar
Probability density function evaluated at `x`
Notes
-----
%(_doc_callparams_note)s
"""
return np.exp(self.logpmf(x, n, p))
def mean(self, n, p):
"""
Mean of the Multinomial distribution
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
mean : float
The mean of the distribution
"""
n, p, npcond = self._process_parameters(n, p)
result = n[..., np.newaxis]*p
return self._checkresult(result, npcond, np.NAN)
def cov(self, n, p):
"""
Covariance matrix of the multinomial distribution.
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
cov : ndarray
The covariance matrix of the distribution
"""
n, p, npcond = self._process_parameters(n, p)
nn = n[..., np.newaxis, np.newaxis]
result = nn * np.einsum('...j,...k->...jk', -p, p)
# change the diagonal
for i in range(p.shape[-1]):
result[..., i, i] += n*p[..., i]
return self._checkresult(result, npcond, np.nan)
def entropy(self, n, p):
r"""
Compute the entropy of the multinomial distribution.
The entropy is computed using this expression:
.. math::
f(x) = - \log n! - n\sum_{i=1}^k p_i \log p_i +
\sum_{i=1}^k \sum_{x=0}^n \binom n x p_i^x(1-p_i)^{n-x} \log x!
Parameters
----------
%(_doc_default_callparams)s
Returns
-------
h : scalar
Entropy of the Multinomial distribution
Notes
-----
%(_doc_callparams_note)s
"""
n, p, npcond = self._process_parameters(n, p)
x = np.r_[1:np.max(n)+1]
term1 = n*np.sum(entr(p), axis=-1)
term1 -= gammaln(n+1)
n = n[..., np.newaxis]
new_axes_needed = max(p.ndim, n.ndim) - x.ndim + 1
x.shape += (1,)*new_axes_needed
term2 = np.sum(binom.pmf(x, n, p)*gammaln(x+1),
axis=(-1, -1-new_axes_needed))
return self._checkresult(term1 + term2, npcond, np.nan)
def rvs(self, n, p, size=None, random_state=None):
"""
Draw random samples from a Multinomial distribution.
Parameters
----------
%(_doc_default_callparams)s
size : integer or iterable of integers, optional
Number of samples to draw (default 1).
%(_doc_random_state)s
Returns
-------
rvs : ndarray or scalar
Random variates of shape (`size`, `len(p)`)
Notes
-----
%(_doc_callparams_note)s
"""
n, p, npcond = self._process_parameters(n, p)
random_state = self._get_random_state(random_state)
return random_state.multinomial(n, p, size)
multinomial = multinomial_gen()
class multinomial_frozen(multi_rv_frozen):
r"""
Create a frozen Multinomial distribution.
Parameters
----------
n : int
number of trials
p: array_like
probability of a trial falling into each category; should sum to 1
seed : None or int or np.random.RandomState instance, optional
This parameter defines the RandomState object to use for drawing
random variates.
If None (or np.random), the global np.random state is used.
If integer, it is used to seed the local RandomState instance
Default is None.
"""
def __init__(self, n, p, seed=None):
self._dist = multinomial_gen(seed)
self.n, self.p, self.npcond = self._dist._process_parameters(n, p)
# monkey patch self._dist
def _process_parameters(n, p):
return self.n, self.p, self.npcond
self._dist._process_parameters = _process_parameters
def logpmf(self, x):
return self._dist.logpmf(x, self.n, self.p)
def pmf(self, x):
return self._dist.pmf(x, self.n, self.p)
def mean(self):
return self._dist.mean(self.n, self.p)
def cov(self):
return self._dist.cov(self.n, self.p)
def entropy(self):
return self._dist.entropy(self.n, self.p)
def rvs(self, size=1, random_state=None):
return self._dist.rvs(self.n, self.p, size, random_state)
# Set frozen generator docstrings from corresponding docstrings in
# multinomial and fill in default strings in class docstrings
for name in ['logpmf', 'pmf', 'mean', 'cov', 'rvs']:
method = multinomial_gen.__dict__[name]
method_frozen = multinomial_frozen.__dict__[name]
method_frozen.__doc__ = doccer.docformat(
method.__doc__, multinomial_docdict_noparams)
method.__doc__ = doccer.docformat(method.__doc__,
multinomial_docdict_params)
class special_ortho_group_gen(multi_rv_generic):
r"""
A matrix-valued SO(N) random variable.
Return a random rotation matrix, drawn from the Haar distribution
(the only uniform distribution on SO(n)).
The `dim` keyword specifies the dimension N.
Methods
-------
``rvs(dim=None, size=1, random_state=None)``
Draw random samples from SO(N).
Parameters
----------
dim : scalar
Dimension of matrices
Notes
----------
This class is wrapping the random_rot code from the MDP Toolkit,
https://github.com/mdp-toolkit/mdp-toolkit
Return a random rotation matrix, drawn from the Haar distribution
(the only uniform distribution on SO(n)).
The algorithm is described in the paper
Stewart, G.W., "The efficient generation of random orthogonal
matrices with an application to condition estimators", SIAM Journal
on Numerical Analysis, 17(3), pp. 403-409, 1980.
For more information see
https://en.wikipedia.org/wiki/Orthogonal_matrix#Randomization
See also the similar `ortho_group`.
Examples
--------
>>> from scipy.stats import special_ortho_group
>>> x = special_ortho_group.rvs(3)
>>> np.dot(x, x.T)
array([[ 1.00000000e+00, 1.13231364e-17, -2.86852790e-16],
[ 1.13231364e-17, 1.00000000e+00, -1.46845020e-16],
[ -2.86852790e-16, -1.46845020e-16, 1.00000000e+00]])
>>> import scipy.linalg
>>> scipy.linalg.det(x)
1.0
This generates one random matrix from SO(3). It is orthogonal and
has a determinant of 1.
"""
def __init__(self, seed=None):
super(special_ortho_group_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__)
def __call__(self, dim=None, seed=None):
"""
Create a frozen SO(N) distribution.
See `special_ortho_group_frozen` for more information.
"""
return special_ortho_group_frozen(dim, seed=seed)
def _process_parameters(self, dim):
"""
Dimension N must be specified; it cannot be inferred.
"""
if dim is None or not np.isscalar(dim) or dim <= 1 or dim != int(dim):
raise ValueError("""Dimension of rotation must be specified,
and must be a scalar greater than 1.""")
return dim
def rvs(self, dim, size=1, random_state=None):
"""
Draw random samples from SO(N).
Parameters
----------
dim : integer
Dimension of rotation space (N).
size : integer, optional
Number of samples to draw (default 1).
Returns
-------
rvs : ndarray or scalar
Random size N-dimensional matrices, dimension (size, dim, dim)
"""
random_state = self._get_random_state(random_state)
size = int(size)
if size > 1:
return np.array([self.rvs(dim, size=1, random_state=random_state)
for i in range(size)])
dim = self._process_parameters(dim)
H = np.eye(dim)
D = np.empty((dim,))
for n in range(dim-1):
x = random_state.normal(size=(dim-n,))
D[n] = np.sign(x[0]) if x[0] != 0 else 1
x[0] += D[n]*np.sqrt((x*x).sum())
# Householder transformation
Hx = (np.eye(dim-n) - 2.*np.outer(x, x)/(x*x).sum())
mat = np.eye(dim)
mat[n:, n:] = Hx
H = np.dot(H, mat)
D[-1] = (-1)**(dim-1)*D[:-1].prod()
# Equivalent to np.dot(np.diag(D), H) but faster, apparently
H = (D*H.T).T
return H
special_ortho_group = special_ortho_group_gen()
class special_ortho_group_frozen(multi_rv_frozen):
def __init__(self, dim=None, seed=None):
"""
Create a frozen SO(N) distribution.
Parameters
----------
dim : scalar
Dimension of matrices
seed : None or int or np.random.RandomState instance, optional
This parameter defines the RandomState object to use for drawing
random variates.
If None (or np.random), the global np.random state is used.
If integer, it is used to seed the local RandomState instance
Default is None.
Examples
--------
>>> from scipy.stats import special_ortho_group
>>> g = special_ortho_group(5)
>>> x = g.rvs()
"""
self._dist = special_ortho_group_gen(seed)
self.dim = self._dist._process_parameters(dim)
def rvs(self, size=1, random_state=None):
return self._dist.rvs(self.dim, size, random_state)
class ortho_group_gen(multi_rv_generic):
r"""
A matrix-valued O(N) random variable.
Return a random orthogonal matrix, drawn from the O(N) Haar
distribution (the only uniform distribution on O(N)).
The `dim` keyword specifies the dimension N.
Methods
-------
``rvs(dim=None, size=1, random_state=None)``
Draw random samples from O(N).
Parameters
----------
dim : scalar
Dimension of matrices
Notes
----------
This class is closely related to `special_ortho_group`.
Some care is taken to avoid numerical error, as per the paper by Mezzadri.
References
----------
.. [1] F. Mezzadri, "How to generate random matrices from the classical
compact groups", :arXiv:`math-ph/0609050v2`.
Examples
--------
>>> from scipy.stats import ortho_group
>>> x = ortho_group.rvs(3)
>>> np.dot(x, x.T)
array([[ 1.00000000e+00, 1.13231364e-17, -2.86852790e-16],
[ 1.13231364e-17, 1.00000000e+00, -1.46845020e-16],
[ -2.86852790e-16, -1.46845020e-16, 1.00000000e+00]])
>>> import scipy.linalg
>>> np.fabs(scipy.linalg.det(x))
1.0
This generates one random matrix from O(3). It is orthogonal and
has a determinant of +1 or -1.
"""
def __init__(self, seed=None):
super(ortho_group_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__)
def _process_parameters(self, dim):
"""
Dimension N must be specified; it cannot be inferred.
"""
if dim is None or not np.isscalar(dim) or dim <= 1 or dim != int(dim):
raise ValueError("Dimension of rotation must be specified,"
"and must be a scalar greater than 1.")
return dim
def rvs(self, dim, size=1, random_state=None):
"""
Draw random samples from O(N).
Parameters
----------
dim : integer
Dimension of rotation space (N).
size : integer, optional
Number of samples to draw (default 1).
Returns
-------
rvs : ndarray or scalar
Random size N-dimensional matrices, dimension (size, dim, dim)
"""
random_state = self._get_random_state(random_state)
size = int(size)
if size > 1:
return np.array([self.rvs(dim, size=1, random_state=random_state)
for i in range(size)])
dim = self._process_parameters(dim)
H = np.eye(dim)
for n in range(dim):
x = random_state.normal(size=(dim-n,))
# random sign, 50/50, but chosen carefully to avoid roundoff error
D = np.sign(x[0]) if x[0] != 0 else 1
x[0] += D*np.sqrt((x*x).sum())
# Householder transformation
Hx = -D*(np.eye(dim-n) - 2.*np.outer(x, x)/(x*x).sum())
mat = np.eye(dim)
mat[n:, n:] = Hx
H = np.dot(H, mat)
return H
ortho_group = ortho_group_gen()
class random_correlation_gen(multi_rv_generic):
r"""
A random correlation matrix.
Return a random correlation matrix, given a vector of eigenvalues.
The `eigs` keyword specifies the eigenvalues of the correlation matrix,
and implies the dimension.
Methods
-------
``rvs(eigs=None, random_state=None)``
Draw random correlation matrices, all with eigenvalues eigs.
Parameters
----------
eigs : 1d ndarray
Eigenvalues of correlation matrix.
Notes
----------
Generates a random correlation matrix following a numerically stable
algorithm spelled out by Davies & Higham. This algorithm uses a single O(N)
similarity transformation to construct a symmetric positive semi-definite
matrix, and applies a series of Givens rotations to scale it to have ones
on the diagonal.
References
----------
.. [1] Davies, Philip I; Higham, Nicholas J; "Numerically stable generation
of correlation matrices and their factors", BIT 2000, Vol. 40,
No. 4, pp. 640 651
Examples
--------
>>> from scipy.stats import random_correlation
>>> np.random.seed(514)
>>> x = random_correlation.rvs((.5, .8, 1.2, 1.5))
>>> x
array([[ 1. , -0.20387311, 0.18366501, -0.04953711],
[-0.20387311, 1. , -0.24351129, 0.06703474],
[ 0.18366501, -0.24351129, 1. , 0.38530195],
[-0.04953711, 0.06703474, 0.38530195, 1. ]])
>>> import scipy.linalg
>>> e, v = scipy.linalg.eigh(x)
>>> e
array([ 0.5, 0.8, 1.2, 1.5])
"""
def __init__(self, seed=None):
super(random_correlation_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__)
def _process_parameters(self, eigs, tol):
eigs = np.asarray(eigs, dtype=float)
dim = eigs.size
if eigs.ndim != 1 or eigs.shape[0] != dim or dim <= 1:
raise ValueError("Array 'eigs' must be a vector of length "
"greater than 1.")
if np.fabs(np.sum(eigs) - dim) > tol:
raise ValueError("Sum of eigenvalues must equal dimensionality.")
for x in eigs:
if x < -tol:
raise ValueError("All eigenvalues must be non-negative.")
return dim, eigs
def _givens_to_1(self, aii, ajj, aij):
"""Computes a 2x2 Givens matrix to put 1's on the diagonal.
The input matrix is a 2x2 symmetric matrix M = [ aii aij ; aij ajj ].
The output matrix g is a 2x2 anti-symmetric matrix of the form
[ c s ; -s c ]; the elements c and s are returned.
Applying the output matrix to the input matrix (as b=g.T M g)
results in a matrix with bii=1, provided tr(M) - det(M) >= 1
and floating point issues do not occur. Otherwise, some other
valid rotation is returned. When tr(M)==2, also bjj=1.
"""
aiid = aii - 1.
ajjd = ajj - 1.
if ajjd == 0:
# ajj==1, so swap aii and ajj to avoid division by zero
return 0., 1.
dd = math.sqrt(max(aij**2 - aiid*ajjd, 0))
# The choice of t should be chosen to avoid cancellation [1]
t = (aij + math.copysign(dd, aij)) / ajjd
c = 1. / math.sqrt(1. + t*t)
if c == 0:
# Underflow
s = 1.0
else:
s = c*t
return c, s
def _to_corr(self, m):
"""
Given a psd matrix m, rotate to put one's on the diagonal, turning it
into a correlation matrix. This also requires the trace equal the
dimensionality. Note: modifies input matrix
"""
# Check requirements for in-place Givens
if not (m.flags.c_contiguous and m.dtype == np.float64 and
m.shape[0] == m.shape[1]):
raise ValueError()
d = m.shape[0]
for i in range(d-1):
if m[i, i] == 1:
continue
elif m[i, i] > 1:
for j in range(i+1, d):
if m[j, j] < 1:
break
else:
for j in range(i+1, d):
if m[j, j] > 1:
break
c, s = self._givens_to_1(m[i, i], m[j, j], m[i, j])
# Use BLAS to apply Givens rotations in-place. Equivalent to:
# g = np.eye(d)
# g[i, i] = g[j,j] = c
# g[j, i] = -s; g[i, j] = s
# m = np.dot(g.T, np.dot(m, g))
mv = m.ravel()
drot(mv, mv, c, -s, n=d,
offx=i*d, incx=1, offy=j*d, incy=1,
overwrite_x=True, overwrite_y=True)
drot(mv, mv, c, -s, n=d,
offx=i, incx=d, offy=j, incy=d,
overwrite_x=True, overwrite_y=True)
return m
def rvs(self, eigs, random_state=None, tol=1e-13, diag_tol=1e-7):
"""
Draw random correlation matrices
Parameters
----------
eigs : 1d ndarray
Eigenvalues of correlation matrix
tol : float, optional
Tolerance for input parameter checks
diag_tol : float, optional
Tolerance for deviation of the diagonal of the resulting
matrix. Default: 1e-7
Raises
------
RuntimeError
Floating point error prevented generating a valid correlation
matrix.
Returns
-------
rvs : ndarray or scalar
Random size N-dimensional matrices, dimension (size, dim, dim),
each having eigenvalues eigs.
"""
dim, eigs = self._process_parameters(eigs, tol=tol)
random_state = self._get_random_state(random_state)
m = ortho_group.rvs(dim, random_state=random_state)
m = np.dot(np.dot(m, np.diag(eigs)), m.T) # Set the trace of m
m = self._to_corr(m) # Carefully rotate to unit diagonal
# Check diagonal
if abs(m.diagonal() - 1).max() > diag_tol:
raise RuntimeError("Failed to generate a valid correlation matrix")
return m
random_correlation = random_correlation_gen()
class unitary_group_gen(multi_rv_generic):
r"""
A matrix-valued U(N) random variable.
Return a random unitary matrix.
The `dim` keyword specifies the dimension N.
Methods
-------
``rvs(dim=None, size=1, random_state=None)``
Draw random samples from U(N).
Parameters
----------
dim : scalar
Dimension of matrices
Notes
----------
This class is similar to `ortho_group`.
References
----------
.. [1] F. Mezzadri, "How to generate random matrices from the classical
compact groups", arXiv:math-ph/0609050v2.
Examples
--------
>>> from scipy.stats import unitary_group
>>> x = unitary_group.rvs(3)
>>> np.dot(x, x.conj().T)
array([[ 1.00000000e+00, 1.13231364e-17, -2.86852790e-16],
[ 1.13231364e-17, 1.00000000e+00, -1.46845020e-16],
[ -2.86852790e-16, -1.46845020e-16, 1.00000000e+00]])
This generates one random matrix from U(3). The dot product confirms that
it is unitary up to machine precision.
"""
def __init__(self, seed=None):
super(unitary_group_gen, self).__init__(seed)
self.__doc__ = doccer.docformat(self.__doc__)
def _process_parameters(self, dim):
"""
Dimension N must be specified; it cannot be inferred.
"""
if dim is None or not np.isscalar(dim) or dim <= 1 or dim != int(dim):
raise ValueError("Dimension of rotation must be specified,"
"and must be a scalar greater than 1.")
return dim
def rvs(self, dim, size=1, random_state=None):
"""
Draw random samples from U(N).
Parameters
----------
dim : integer
Dimension of space (N).
size : integer, optional
Number of samples to draw (default 1).
Returns
-------
rvs : ndarray or scalar
Random size N-dimensional matrices, dimension (size, dim, dim)
"""
random_state = self._get_random_state(random_state)
size = int(size)
if size > 1:
return np.array([self.rvs(dim, size=1, random_state=random_state)
for i in range(size)])
dim = self._process_parameters(dim)
z = 1/math.sqrt(2)*(random_state.normal(size=(dim, dim)) +
1j*random_state.normal(size=(dim, dim)))
q, r = scipy.linalg.qr(z)
d = r.diagonal()
q *= d/abs(d)
return q
unitary_group = unitary_group_gen()