class GaussianProcessClassifier(BaseEstimator, ClassifierMixin):
"""Gaussian process classification (GPC) based on Laplace approximation.
The implementation is based on Algorithm 3.1, 3.2, and 5.1 of
Gaussian Processes for Machine Learning (GPML) by Rasmussen and
Williams.
Internally, the Laplace approximation is used for approximating the
non-Gaussian posterior by a Gaussian.
Currently, the implementation is restricted to using the logistic link
function. For multi-class classification, several binary one-versus rest
classifiers are fitted. Note that this class thus does not implement
a true multi-class Laplace approximation.
Parameters
----------
kernel : kernel object
The kernel specifying the covariance function of the GP. If None is
passed, the kernel "1.0 * RBF(1.0)" is used as default. Note that
the kernel's hyperparameters are optimized during fitting.
optimizer : string or callable, optional (default: "fmin_l_bfgs_b")
Can either be one of the internally supported optimizers for optimizing
the kernel's parameters, specified by a string, or an externally
defined optimizer passed as a callable. If a callable is passed, it
must have the signature::
def optimizer(obj_func, initial_theta, bounds):
# * 'obj_func' is the objective function to be maximized, which
# takes the hyperparameters theta as parameter and an
# optional flag eval_gradient, which determines if the
# gradient is returned additionally to the function value
# * 'initial_theta': the initial value for theta, which can be
# used by local optimizers
# * 'bounds': the bounds on the values of theta
....
# Returned are the best found hyperparameters theta and
# the corresponding value of the target function.
return theta_opt, func_min
Per default, the 'fmin_l_bfgs_b' algorithm from scipy.optimize
is used. If None is passed, the kernel's parameters are kept fixed.
Available internal optimizers are::
'fmin_l_bfgs_b'
n_restarts_optimizer : int, optional (default: 0)
The number of restarts of the optimizer for finding the kernel's
parameters which maximize the log-marginal likelihood. The first run
of the optimizer is performed from the kernel's initial parameters,
the remaining ones (if any) from thetas sampled log-uniform randomly
from the space of allowed theta-values. If greater than 0, all bounds
must be finite. Note that n_restarts_optimizer=0 implies that one
run is performed.
max_iter_predict : int, optional (default: 100)
The maximum number of iterations in Newton's method for approximating
the posterior during predict. Smaller values will reduce computation
time at the cost of worse results.
warm_start : bool, optional (default: False)
If warm-starts are enabled, the solution of the last Newton iteration
on the Laplace approximation of the posterior mode is used as
initialization for the next call of _posterior_mode(). This can speed
up convergence when _posterior_mode is called several times on similar
problems as in hyperparameter optimization.
copy_X_train : bool, optional (default: True)
If True, a persistent copy of the training data is stored in the
object. Otherwise, just a reference to the training data is stored,
which might cause predictions to change if the data is modified
externally.
random_state : integer or numpy.RandomState, optional
The generator used to initialize the centers. If an integer is
given, it fixes the seed. Defaults to the global numpy random
number generator.
multi_class: string, default : "one_vs_rest"
Specifies how multi-class classification problems are handled.
Supported are "one_vs_rest" and "one_vs_one". In "one_vs_rest",
one binary Gaussian process classifier is fitted for each class, which
is trained to separate this class from the rest. In "one_vs_one", one
binary Gaussian process classifier is fitted for each pair of classes,
which is trained to separate these two classes. The predictions of
these binary predictors are combined into multi-class predictions.
Note that "one_vs_one" does not support predicting probability
estimates.
n_jobs : int, optional, default: 1
The number of jobs to use for the computation. If -1 all CPUs are used.
If 1 is given, no parallel computing code is used at all, which is
useful for debugging. For n_jobs below -1, (n_cpus + 1 + n_jobs) are
used. Thus for n_jobs = -2, all CPUs but one are used.
Attributes
----------
kernel_ : kernel object
The kernel used for prediction. In case of binary classification,
the structure of the kernel is the same as the one passed as parameter
but with optimized hyperparameters. In case of multi-class
classification, a CompoundKernel is returned which consists of the
different kernels used in the one-versus-rest classifiers.
log_marginal_likelihood_value_ : float
The log-marginal-likelihood of ``self.kernel_.theta``
classes_ : array-like, shape = (n_classes,)
Unique class labels.
n_classes_ : int
The number of classes in the training data
.. versionadded:: 0.18
"""
def __init__(self, kernel=None, optimizer="fmin_l_bfgs_b",
n_restarts_optimizer=0, max_iter_predict=100,
warm_start=False, copy_X_train=True, random_state=None,
multi_class="one_vs_rest", n_jobs=1):
self.kernel = kernel
self.optimizer = optimizer
self.n_restarts_optimizer = n_restarts_optimizer
self.max_iter_predict = max_iter_predict
self.warm_start = warm_start
self.copy_X_train = copy_X_train
self.random_state = random_state
self.multi_class = multi_class
self.n_jobs = n_jobs
def fit(self, X, y):
"""Fit Gaussian process classification model
Parameters
----------
X : array-like, shape = (n_samples, n_features)
Training data
y : array-like, shape = (n_samples,)
Target values, must be binary
Returns
-------
self : returns an instance of self.
"""
X, y = check_X_y(X, y, multi_output=False)
self.base_estimator_ = _BinaryGaussianProcessClassifierLaplace(
self.kernel, self.optimizer, self.n_restarts_optimizer,
self.max_iter_predict, self.warm_start, self.copy_X_train,
self.random_state)
self.classes_ = np.unique(y)
self.n_classes_ = self.classes_.size
if self.n_classes_ == 1:
raise ValueError("GaussianProcessClassifier requires 2 or more "
"distinct classes. Only class %s present."
% self.classes_[0])
if self.n_classes_ > 2:
if self.multi_class == "one_vs_rest":
self.base_estimator_ = \
OneVsRestClassifier(self.base_estimator_,
n_jobs=self.n_jobs)
elif self.multi_class == "one_vs_one":
self.base_estimator_ = \
OneVsOneClassifier(self.base_estimator_,
n_jobs=self.n_jobs)
else:
raise ValueError("Unknown multi-class mode %s"
% self.multi_class)
self.base_estimator_.fit(X, y)
if self.n_classes_ > 2:
self.log_marginal_likelihood_value_ = np.mean(
[estimator.log_marginal_likelihood()
for estimator in self.base_estimator_.estimators_])
else:
self.log_marginal_likelihood_value_ = \
self.base_estimator_.log_marginal_likelihood()
return self
def predict(self, X):
"""Perform classification on an array of test vectors X.
Parameters
----------
X : array-like, shape = (n_samples, n_features)
Returns
-------
C : array, shape = (n_samples,)
Predicted target values for X, values are from ``classes_``
"""
check_is_fitted(self, ["classes_", "n_classes_"])
X = check_array(X)
return self.base_estimator_.predict(X)
def predict_proba(self, X):
"""Return probability estimates for the test vector X.
Parameters
----------
X : array-like, shape = (n_samples, n_features)
Returns
-------
C : array-like, shape = (n_samples, n_classes)
Returns the probability of the samples for each class in
the model. The columns correspond to the classes in sorted
order, as they appear in the attribute `classes_`.
"""
check_is_fitted(self, ["classes_", "n_classes_"])
if self.n_classes_ > 2 and self.multi_class == "one_vs_one":
raise ValueError("one_vs_one multi-class mode does not support "
"predicting probability estimates. Use "
"one_vs_rest mode instead.")
X = check_array(X)
return self.base_estimator_.predict_proba(X)
@property
def kernel_(self):
if self.n_classes_ == 2:
return self.base_estimator_.kernel_
else:
return CompoundKernel(
[estimator.kernel_
for estimator in self.base_estimator_.estimators_])
def log_marginal_likelihood(self, theta=None, eval_gradient=False):
"""Returns log-marginal likelihood of theta for training data.
In the case of multi-class classification, the mean log-marginal
likelihood of the one-versus-rest classifiers are returned.
Parameters
----------
theta : array-like, shape = (n_kernel_params,) or none
Kernel hyperparameters for which the log-marginal likelihood is
evaluated. In the case of multi-class classification, theta may
be the hyperparameters of the compound kernel or of an individual
kernel. In the latter case, all individual kernel get assigned the
same theta values. If None, the precomputed log_marginal_likelihood
of ``self.kernel_.theta`` is returned.
eval_gradient : bool, default: False
If True, the gradient of the log-marginal likelihood with respect
to the kernel hyperparameters at position theta is returned
additionally. Note that gradient computation is not supported
for non-binary classification. If True, theta must not be None.
Returns
-------
log_likelihood : float
Log-marginal likelihood of theta for training data.
log_likelihood_gradient : array, shape = (n_kernel_params,), optional
Gradient of the log-marginal likelihood with respect to the kernel
hyperparameters at position theta.
Only returned when eval_gradient is True.
"""
check_is_fitted(self, ["classes_", "n_classes_"])
if theta is None:
if eval_gradient:
raise ValueError(
"Gradient can only be evaluated for theta!=None")
return self.log_marginal_likelihood_value_
theta = np.asarray(theta)
if self.n_classes_ == 2:
return self.base_estimator_.log_marginal_likelihood(
theta, eval_gradient)
else:
if eval_gradient:
raise NotImplementedError(
"Gradient of log-marginal-likelihood not implemented for "
"multi-class GPC.")
estimators = self.base_estimator_.estimators_
n_dims = estimators[0].kernel_.n_dims
if theta.shape[0] == n_dims: # use same theta for all sub-kernels
return np.mean(
[estimator.log_marginal_likelihood(theta)
for i, estimator in enumerate(estimators)])
elif theta.shape[0] == n_dims * self.classes_.shape[0]:
# theta for compound kernel
return np.mean(
[estimator.log_marginal_likelihood(
theta[n_dims * i:n_dims * (i + 1)])
for i, estimator in enumerate(estimators)])
else:
raise ValueError("Shape of theta must be either %d or %d. "
"Obtained theta with shape %d."
% (n_dims, n_dims * self.classes_.shape[0],
theta.shape[0]))
class GaussianProcessClassifier(BaseEstimator, ClassifierMixin):
"""Gaussian process classification (GPC) based on Laplace approximation.
The implementation is based on Algorithm 3.1, 3.2, and 5.1 of
Gaussian Processes for Machine Learning (GPML) by Rasmussen and
Williams.
Internally, the Laplace approximation is used for approximating the
non-Gaussian posterior by a Gaussian.
Currently, the implementation is restricted to using the logistic link
function. For multi-class classification, several binary one-versus rest
classifiers are fitted. Note that this class thus does not implement
a true multi-class Laplace approximation.
Parameters
----------
kernel : kernel object
The kernel specifying the covariance function of the GP. If None is
passed, the kernel "1.0 * RBF(1.0)" is used as default. Note that
the kernel's hyperparameters are optimized during fitting.
optimizer : string or callable, optional (default: "fmin_l_bfgs_b")
Can either be one of the internally supported optimizers for optimizing
the kernel's parameters, specified by a string, or an externally
defined optimizer passed as a callable. If a callable is passed, it
must have the signature::
def optimizer(obj_func, initial_theta, bounds):
# * 'obj_func' is the objective function to be maximized, which
# takes the hyperparameters theta as parameter and an
# optional flag eval_gradient, which determines if the
# gradient is returned additionally to the function value
# * 'initial_theta': the initial value for theta, which can be
# used by local optimizers
# * 'bounds': the bounds on the values of theta
....
# Returned are the best found hyperparameters theta and
# the corresponding value of the target function.
return theta_opt, func_min
Per default, the 'fmin_l_bfgs_b' algorithm from scipy.optimize
is used. If None is passed, the kernel's parameters are kept fixed.
Available internal optimizers are::
'fmin_l_bfgs_b'
n_restarts_optimizer: int, optional (default: 0)
The number of restarts of the optimizer for finding the kernel's
parameters which maximize the log-marginal likelihood. The first run
of the optimizer is performed from the kernel's initial parameters,
the remaining ones (if any) from thetas sampled log-uniform randomly
from the space of allowed theta-values. If greater than 0, all bounds
must be finite. Note that n_restarts_optimizer=0 implies that one
run is performed.
max_iter_predict: int, optional (default: 100)
The maximum number of iterations in Newton's method for approximating
the posterior during predict. Smaller values will reduce computation
time at the cost of worse results.
warm_start : bool, optional (default: False)
If warm-starts are enabled, the solution of the last Newton iteration
on the Laplace approximation of the posterior mode is used as
initialization for the next call of _posterior_mode(). This can speed
up convergence when _posterior_mode is called several times on similar
problems as in hyperparameter optimization.
copy_X_train : bool, optional (default: True)
If True, a persistent copy of the training data is stored in the
object. Otherwise, just a reference to the training data is stored,
which might cause predictions to change if the data is modified
externally.
random_state : integer or numpy.RandomState, optional
The generator used to initialize the centers. If an integer is
given, it fixes the seed. Defaults to the global numpy random
number generator.
multi_class: string, default: "one_vs_rest"
Specifies how multi-class classification problems are handled.
Supported are "one_vs_rest" and "one_vs_one". In "one_vs_rest",
one binary Gaussian process classifier is fitted for each class, which
is trained to separate this class from the rest. In "one_vs_one", one
binary Gaussian process classifier is fitted for each pair of classes,
which is trained to separate these two classes. The predictions of
these binary predictors are combined into multi-class predictions.
Note that "one_vs_one" does not support predicting probability
estimates.
n_jobs : int, optional, default: 1
The number of jobs to use for the computation. If -1 all CPUs are used.
If 1 is given, no parallel computing code is used at all, which is
useful for debugging. For n_jobs below -1, (n_cpus + 1 + n_jobs) are
used. Thus for n_jobs = -2, all CPUs but one are used.
Attributes
----------
kernel_ : kernel object
The kernel used for prediction. In case of binary classification,
the structure of the kernel is the same as the one passed as parameter
but with optimized hyperparameters. In case of multi-class
classification, a CompoundKernel is returned which consists of the
different kernels used in the one-versus-rest classifiers.
log_marginal_likelihood_value_: float
The log-marginal-likelihood of ``self.kernel_.theta``
classes_ : array-like, shape = (n_classes,)
Unique class labels.
n_classes_ : int
The number of classes in the training data
"""
def __init__(self,
kernel=None,
optimizer="fmin_l_bfgs_b",
n_restarts_optimizer=0,
max_iter_predict=100,
warm_start=False,
copy_X_train=True,
random_state=None,
multi_class="one_vs_rest",
n_jobs=1):
self.kernel = kernel
self.optimizer = optimizer
self.n_restarts_optimizer = n_restarts_optimizer
self.max_iter_predict = max_iter_predict
self.warm_start = warm_start
self.copy_X_train = copy_X_train
self.random_state = random_state
self.multi_class = multi_class
self.n_jobs = n_jobs
def fit(self, X, y):
"""Fit Gaussian process classification model
Parameters
----------
X : array-like, shape = (n_samples, n_features)
Training data
y : array-like, shape = (n_samples,)
Target values, must be binary
Returns
-------
self : returns an instance of self.
"""
X, y = check_X_y(X, y, multi_output=False)
self.base_estimator_ = _BinaryGaussianProcessClassifierLaplace(
self.kernel, self.optimizer, self.n_restarts_optimizer,
self.max_iter_predict, self.warm_start, self.copy_X_train,
self.random_state)
self.classes_ = np.unique(y)
self.n_classes_ = self.classes_.size
if self.n_classes_ == 1:
raise ValueError("GaussianProcessClassifier requires 2 or more "
"distinct classes. Only class %s present." %
self.classes_[0])
if self.n_classes_ > 2:
if self.multi_class == "one_vs_rest":
self.base_estimator_ = \
OneVsRestClassifier(self.base_estimator_,
n_jobs=self.n_jobs)
elif self.multi_class == "one_vs_one":
self.base_estimator_ = \
OneVsOneClassifier(self.base_estimator_,
n_jobs=self.n_jobs)
else:
raise ValueError("Unknown multi-class mode %s" %
self.multi_class)
self.base_estimator_.fit(X, y)
if self.n_classes_ > 2:
self.log_marginal_likelihood_value_ = np.mean([
estimator.log_marginal_likelihood()
for estimator in self.base_estimator_.estimators_
])
else:
self.log_marginal_likelihood_value_ = \
self.base_estimator_.log_marginal_likelihood()
return self
def predict(self, X):
"""Perform classification on an array of test vectors X.
Parameters
----------
X : array-like, shape = (n_samples, n_features)
Returns
-------
C : array, shape = (n_samples,)
Predicted target values for X, values are from ``classes_``
"""
check_is_fitted(self, ["classes_", "n_classes_"])
X = check_array(X)
return self.base_estimator_.predict(X)
def predict_proba(self, X):
"""Return probability estimates for the test vector X.
Parameters
----------
X : array-like, shape = (n_samples, n_features)
Returns
-------
C : array-like, shape = (n_samples, n_classes)
Returns the probability of the samples for each class in
the model. The columns correspond to the classes in sorted
order, as they appear in the attribute `classes_`.
"""
check_is_fitted(self, ["classes_", "n_classes_"])
if self.n_classes_ > 2 and self.multi_class == "one_vs_one":
raise ValueError("one_vs_one multi-class mode does not support "
"predicting probability estimates. Use "
"one_vs_rest mode instead.")
X = check_array(X)
return self.base_estimator_.predict_proba(X)
@property
def kernel_(self):
if self.n_classes_ == 2:
return self.base_estimator_.kernel_
else:
return CompoundKernel([
estimator.kernel_
for estimator in self.base_estimator_.estimators_
])
def log_marginal_likelihood(self, theta=None, eval_gradient=False):
"""Returns log-marginal likelihood of theta for training data.
In the case of multi-class classification, the mean log-marginal
likelihood of the one-versus-rest classifiers are returned.
Parameters
----------
theta : array-like, shape = (n_kernel_params,) or none
Kernel hyperparameters for which the log-marginal likelihood is
evaluated. In the case of multi-class classification, theta may
be the hyperparameters of the compound kernel or of an individual
kernel. In the latter case, all individual kernel get assigned the
same theta values. If None, the precomputed log_marginal_likelihood
of ``self.kernel_.theta`` is returned.
eval_gradient : bool, default: False
If True, the gradient of the log-marginal likelihood with respect
to the kernel hyperparameters at position theta is returned
additionally. Note that gradient computation is not supported
for non-binary classification. If True, theta must not be None.
Returns
-------
log_likelihood : float
Log-marginal likelihood of theta for training data.
log_likelihood_gradient : array, shape = (n_kernel_params,), optional
Gradient of the log-marginal likelihood with respect to the kernel
hyperparameters at position theta.
Only returned when eval_gradient is True.
"""
check_is_fitted(self, ["classes_", "n_classes_"])
if theta is None:
if eval_gradient:
raise ValueError(
"Gradient can only be evaluated for theta!=None")
return self.log_marginal_likelihood_value_
theta = np.asarray(theta)
if self.n_classes_ == 2:
return self.base_estimator_.log_marginal_likelihood(
theta, eval_gradient)
else:
if eval_gradient:
raise NotImplementedError(
"Gradient of log-marginal-likelhood not implemented for "
"multi-class GPC.")
estimators = self.base_estimator_.estimators_
n_dims = estimators[0].kernel_.n_dims
if theta.shape[0] == n_dims: # use same theta for all sub-kernels
return np.mean([
estimator.log_marginal_likelihood(theta)
for i, estimator in enumerate(estimators)
])
elif theta.shape[0] == n_dims * self.classes_.shape[0]:
# theta for compound kernel
return np.mean([
estimator.log_marginal_likelihood(theta[n_dims * i:n_dims *
(i + 1)])
for i, estimator in enumerate(estimators)
])
else:
raise ValueError(
"Shape of theta must be either %d or %d. "
"Obtained theta with shape %d." %
(n_dims, n_dims * self.classes_.shape[0], theta.shape[0]))
class GaussianProcessClassifier(GPC):
def fit(self, X, y):
"""Fit Gaussian process classification model
Parameters
----------
X : sequence of length n_samples
Feature vectors or other representations of training data.
Could either be array-like with shape = (n_samples, n_features)
or a list of objects.
y : array-like of shape (n_samples,)
Target values, must be binary
Returns
-------
self : returns an instance of self.
"""
if self.kernel is None or self.kernel.requires_vector_input:
X, y = check_X_y(X,
y,
multi_output=False,
ensure_2d=True,
dtype="numeric")
else:
X, y = check_X_y(X,
y,
multi_output=False,
ensure_2d=False,
dtype=None)
self.base_estimator_ = BinaryGaussianProcessClassifier(
self.kernel, self.optimizer, self.n_restarts_optimizer,
self.max_iter_predict, self.warm_start, self.copy_X_train,
self.random_state)
self.classes_ = numpy.unique(y)
self.n_classes_ = self.classes_.size
if self.n_classes_ == 1:
raise ValueError("GaussianProcessClassifier requires 2 or more "
"distinct classes; got %d class (only class %s "
"is present)" %
(self.n_classes_, self.classes_[0]))
if self.n_classes_ > 2:
if self.multi_class == "one_vs_rest":
self.base_estimator_ = \
OneVsRestClassifier(self.base_estimator_,
n_jobs=self.n_jobs)
elif self.multi_class == "one_vs_one":
self.base_estimator_ = \
OneVsOneClassifier(self.base_estimator_,
n_jobs=self.n_jobs)
else:
raise ValueError("Unknown multi-class mode %s" %
self.multi_class)
self.base_estimator_.fit(X, y)
if self.n_classes_ > 2:
self.log_marginal_likelihood_value_ = numpy.mean([
estimator.log_marginal_likelihood()
for estimator in self.base_estimator_.estimators_
])
else:
self.log_marginal_likelihood_value_ = \
self.base_estimator_.log_marginal_likelihood()
return self
