projektAI/venv/Lib/site-packages/sklearn/covariance/_empirical_covariance.py
2021-06-06 22:13:05 +02:00

318 lines
10 KiB
Python

"""
Maximum likelihood covariance estimator.
"""
# Author: Alexandre Gramfort <alexandre.gramfort@inria.fr>
# Gael Varoquaux <gael.varoquaux@normalesup.org>
# Virgile Fritsch <virgile.fritsch@inria.fr>
#
# License: BSD 3 clause
# avoid division truncation
import warnings
import numpy as np
from scipy import linalg
from ..base import BaseEstimator
from ..utils import check_array
from ..utils.extmath import fast_logdet
from ..metrics.pairwise import pairwise_distances
from ..utils.validation import _deprecate_positional_args
def log_likelihood(emp_cov, precision):
"""Computes the sample mean of the log_likelihood under a covariance model
computes the empirical expected log-likelihood (accounting for the
normalization terms and scaling), allowing for universal comparison (beyond
this software package)
Parameters
----------
emp_cov : ndarray of shape (n_features, n_features)
Maximum Likelihood Estimator of covariance.
precision : ndarray of shape (n_features, n_features)
The precision matrix of the covariance model to be tested.
Returns
-------
log_likelihood_ : float
Sample mean of the log-likelihood.
"""
p = precision.shape[0]
log_likelihood_ = - np.sum(emp_cov * precision) + fast_logdet(precision)
log_likelihood_ -= p * np.log(2 * np.pi)
log_likelihood_ /= 2.
return log_likelihood_
@_deprecate_positional_args
def empirical_covariance(X, *, assume_centered=False):
"""Computes the Maximum likelihood covariance estimator
Parameters
----------
X : ndarray of shape (n_samples, n_features)
Data from which to compute the covariance estimate
assume_centered : bool, default=False
If True, data will not be centered before computation.
Useful when working with data whose mean is almost, but not exactly
zero.
If False, data will be centered before computation.
Returns
-------
covariance : ndarray of shape (n_features, n_features)
Empirical covariance (Maximum Likelihood Estimator).
Examples
--------
>>> from sklearn.covariance import empirical_covariance
>>> X = [[1,1,1],[1,1,1],[1,1,1],
... [0,0,0],[0,0,0],[0,0,0]]
>>> empirical_covariance(X)
array([[0.25, 0.25, 0.25],
[0.25, 0.25, 0.25],
[0.25, 0.25, 0.25]])
"""
X = np.asarray(X)
if X.ndim == 1:
X = np.reshape(X, (1, -1))
if X.shape[0] == 1:
warnings.warn("Only one sample available. "
"You may want to reshape your data array")
if assume_centered:
covariance = np.dot(X.T, X) / X.shape[0]
else:
covariance = np.cov(X.T, bias=1)
if covariance.ndim == 0:
covariance = np.array([[covariance]])
return covariance
class EmpiricalCovariance(BaseEstimator):
"""Maximum likelihood covariance estimator
Read more in the :ref:`User Guide <covariance>`.
Parameters
----------
store_precision : bool, default=True
Specifies if the estimated precision is stored.
assume_centered : bool, default=False
If True, data are not centered before computation.
Useful when working with data whose mean is almost, but not exactly
zero.
If False (default), data are centered before computation.
Attributes
----------
location_ : ndarray of shape (n_features,)
Estimated location, i.e. the estimated mean.
covariance_ : ndarray of shape (n_features, n_features)
Estimated covariance matrix
precision_ : ndarray of shape (n_features, n_features)
Estimated pseudo-inverse matrix.
(stored only if store_precision is True)
Examples
--------
>>> import numpy as np
>>> from sklearn.covariance import EmpiricalCovariance
>>> from sklearn.datasets import make_gaussian_quantiles
>>> real_cov = np.array([[.8, .3],
... [.3, .4]])
>>> rng = np.random.RandomState(0)
>>> X = rng.multivariate_normal(mean=[0, 0],
... cov=real_cov,
... size=500)
>>> cov = EmpiricalCovariance().fit(X)
>>> cov.covariance_
array([[0.7569..., 0.2818...],
[0.2818..., 0.3928...]])
>>> cov.location_
array([0.0622..., 0.0193...])
"""
@_deprecate_positional_args
def __init__(self, *, store_precision=True, assume_centered=False):
self.store_precision = store_precision
self.assume_centered = assume_centered
def _set_covariance(self, covariance):
"""Saves the covariance and precision estimates
Storage is done accordingly to `self.store_precision`.
Precision stored only if invertible.
Parameters
----------
covariance : array-like of shape (n_features, n_features)
Estimated covariance matrix to be stored, and from which precision
is computed.
"""
covariance = check_array(covariance)
# set covariance
self.covariance_ = covariance
# set precision
if self.store_precision:
self.precision_ = linalg.pinvh(covariance, check_finite=False)
else:
self.precision_ = None
def get_precision(self):
"""Getter for the precision matrix.
Returns
-------
precision_ : array-like of shape (n_features, n_features)
The precision matrix associated to the current covariance object.
"""
if self.store_precision:
precision = self.precision_
else:
precision = linalg.pinvh(self.covariance_, check_finite=False)
return precision
def fit(self, X, y=None):
"""Fits the Maximum Likelihood Estimator covariance model
according to the given training data and parameters.
Parameters
----------
X : array-like of shape (n_samples, n_features)
Training data, where n_samples is the number of samples and
n_features is the number of features.
y : Ignored
Not used, present for API consistency by convention.
Returns
-------
self : object
"""
X = self._validate_data(X)
if self.assume_centered:
self.location_ = np.zeros(X.shape[1])
else:
self.location_ = X.mean(0)
covariance = empirical_covariance(
X, assume_centered=self.assume_centered)
self._set_covariance(covariance)
return self
def score(self, X_test, y=None):
"""Computes the log-likelihood of a Gaussian data set with
`self.covariance_` as an estimator of its covariance matrix.
Parameters
----------
X_test : array-like of shape (n_samples, n_features)
Test data of which we compute the likelihood, where n_samples is
the number of samples and n_features is the number of features.
X_test is assumed to be drawn from the same distribution than
the data used in fit (including centering).
y : Ignored
Not used, present for API consistency by convention.
Returns
-------
res : float
The likelihood of the data set with `self.covariance_` as an
estimator of its covariance matrix.
"""
# compute empirical covariance of the test set
test_cov = empirical_covariance(
X_test - self.location_, assume_centered=True)
# compute log likelihood
res = log_likelihood(test_cov, self.get_precision())
return res
def error_norm(self, comp_cov, norm='frobenius', scaling=True,
squared=True):
"""Computes the Mean Squared Error between two covariance estimators.
(In the sense of the Frobenius norm).
Parameters
----------
comp_cov : array-like of shape (n_features, n_features)
The covariance to compare with.
norm : {"frobenius", "spectral"}, default="frobenius"
The type of norm used to compute the error. Available error types:
- 'frobenius' (default): sqrt(tr(A^t.A))
- 'spectral': sqrt(max(eigenvalues(A^t.A))
where A is the error ``(comp_cov - self.covariance_)``.
scaling : bool, default=True
If True (default), the squared error norm is divided by n_features.
If False, the squared error norm is not rescaled.
squared : bool, default=True
Whether to compute the squared error norm or the error norm.
If True (default), the squared error norm is returned.
If False, the error norm is returned.
Returns
-------
result : float
The Mean Squared Error (in the sense of the Frobenius norm) between
`self` and `comp_cov` covariance estimators.
"""
# compute the error
error = comp_cov - self.covariance_
# compute the error norm
if norm == "frobenius":
squared_norm = np.sum(error ** 2)
elif norm == "spectral":
squared_norm = np.amax(linalg.svdvals(np.dot(error.T, error)))
else:
raise NotImplementedError(
"Only spectral and frobenius norms are implemented")
# optionally scale the error norm
if scaling:
squared_norm = squared_norm / error.shape[0]
# finally get either the squared norm or the norm
if squared:
result = squared_norm
else:
result = np.sqrt(squared_norm)
return result
def mahalanobis(self, X):
"""Computes the squared Mahalanobis distances of given observations.
Parameters
----------
X : array-like of shape (n_samples, n_features)
The observations, the Mahalanobis distances of the which we
compute. Observations are assumed to be drawn from the same
distribution than the data used in fit.
Returns
-------
dist : ndarray of shape (n_samples,)
Squared Mahalanobis distances of the observations.
"""
precision = self.get_precision()
# compute mahalanobis distances
dist = pairwise_distances(X, self.location_[np.newaxis, :],
metric='mahalanobis', VI=precision)
return np.reshape(dist, (len(X),)) ** 2