content: """Gaussian processes classification."""
  
  # Authors: Jan Hendrik Metzen <jhm@informatik.uni-bremen.de>
  #
  # License: BSD 3 clause
  
  import warnings
  from operator import itemgetter
  
  import numpy as np
  from scipy.linalg import cholesky, cho_solve, solve
  from scipy.optimize import fmin_l_bfgs_b
  from scipy.special import erf
  
  from sklearn.base import BaseEstimator, ClassifierMixin, clone
  from sklearn.gaussian_process.kernels \
      import RBF, CompoundKernel, ConstantKernel as C
  from sklearn.utils.validation import check_X_y, check_is_fitted, check_array
  from sklearn.utils import check_random_state
  from sklearn.preprocessing import LabelEncoder
  from sklearn.multiclass import OneVsRestClassifier, OneVsOneClassifier
  
  
  # Values required for approximating the logistic sigmoid by
  # error functions. coefs are obtained via:
  # x = np.array([0, 0.6, 2, 3.5, 4.5, np.inf])
  # b = logistic(x)
  # A = (erf(np.dot(x, self.lambdas)) + 1) / 2
  # coefs = lstsq(A, b)[0]
  LAMBDAS = np.array([0.41, 0.4, 0.37, 0.44, 0.39])[:, np.newaxis]
  COEFS = np.array([-1854.8214151, 3516.89893646, 221.29346712,
                    128.12323805, -2010.49422654])[:, np.newaxis]
  
  
  class _BinaryGaussianProcessClassifierLaplace(BaseEstimator):
      """Binary Gaussian process classification 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.
  
      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.
  
      Attributes
      ----------
      X_train_ : array-like, shape = (n_samples, n_features)
          Feature values in training data (also required for prediction)
  
      y_train_: array-like, shape = (n_samples,)
          Target values in training data (also required for prediction)
  
      classes_ : array-like, shape = (n_classes,)
          Unique class labels.
  
      kernel_: kernel object
          The kernel used for prediction. The structure of the kernel is the
          same as the one passed as parameter but with optimized hyperparameters
  
      L_: array-like, shape = (n_samples, n_samples)
          Lower-triangular Cholesky decomposition of the kernel in X_train_
  
      pi_: array-like, shape = (n_samples,)
          The probabilities of the positive class for the training points
          X_train_
  
      W_sr_: array-like, shape = (n_samples,)
          Square root of W, the Hessian of log-likelihood of the latent function
          values for the observed labels. Since W is diagonal, only the diagonal
          of sqrt(W) is stored.
  
      log_marginal_likelihood_value_: float
          The log-marginal-likelihood of ``self.kernel_.theta``
      """
      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):
          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
  
      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.
          """
          if self.kernel is None:  # Use an RBF kernel as default
              self.kernel_ = C(1.0, constant_value_bounds="fixed") \
                  * RBF(1.0, length_scale_bounds="fixed")
          else:
              self.kernel_ = clone(self.kernel)
  
          self.rng = check_random_state(self.random_state)
  
          self.X_train_ = np.copy(X) if self.copy_X_train else X
  
          # Encode class labels and check that it is a binary classification
          # problem
          label_encoder = LabelEncoder()
          self.y_train_ = label_encoder.fit_transform(y)
          self.classes_ = label_encoder.classes_
          if self.classes_.size > 2:
              raise ValueError("%s supports only binary classification. "
                               "y contains classes %s"
                               % (self.__class__.__name__, self.classes_))
          elif self.classes_.size == 1:
              raise ValueError("{0:s} requires 2 classes.".format(
                  self.__class__.__name__))
  
          if self.optimizer is not None and self.kernel_.n_dims > 0:
              # Choose hyperparameters based on maximizing the log-marginal
              # likelihood (potentially starting from several initial values)
              def obj_func(theta, eval_gradient=True):
                  if eval_gradient:
                      lml, grad = self.log_marginal_likelihood(
                          theta, eval_gradient=True)
                      return -lml, -grad
                  else:
                      return -self.log_marginal_likelihood(theta)
  
              # First optimize starting from theta specified in kernel
              optima = [self._constrained_optimization(obj_func,
                                                       self.kernel_.theta,
                                                       self.kernel_.bounds)]
  
              # Additional runs are performed from log-uniform chosen initial
              # theta
              if self.n_restarts_optimizer > 0:
                  if not np.isfinite(self.kernel_.bounds).all():
                      raise ValueError(
                          "Multiple optimizer restarts (n_restarts_optimizer>0) "
                          "requires that all bounds are finite.")
                  bounds = self.kernel_.bounds
                  for iteration in range(self.n_restarts_optimizer):
                      theta_initial = np.exp(self.rng.uniform(bounds[:, 0],
                                                              bounds[:, 1]))
                      optima.append(
                          self._constrained_optimization(obj_func, theta_initial,
                                                         bounds))
              # Select result from run with minimal (negative) log-marginal
              # likelihood
              lml_values = list(map(itemgetter(1), optima))
              self.kernel_.theta = optima[np.argmin(lml_values)][0]
              self.log_marginal_likelihood_value_ = -np.min(lml_values)
          else:
              self.log_marginal_likelihood_value_ = \
                  self.log_marginal_likelihood(self.kernel_.theta)
  
          # Precompute quantities required for predictions which are independent
          # of actual query points
          K = self.kernel_(self.X_train_)
  
          _, (self.pi_, self.W_sr_, self.L_, _, _) = \
              self._posterior_mode(K, return_temporaries=True)
  
          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, ["X_train_", "y_train_", "pi_", "W_sr_", "L_"])
  
          # As discussed on Section 3.4.2 of GPML, for making hard binary
          # decisions, it is enough to compute the MAP of the posterior and
          # pass it through the link function
          K_star = self.kernel_(self.X_train_, X)  # K_star =k(x_star)
          f_star = K_star.T.dot(self.y_train_ - self.pi_)  # Algorithm 3.2,Line 4
  
          return np.where(f_star > 0, self.classes_[1], self.classes_[0])
  
      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, ["X_train_", "y_train_", "pi_", "W_sr_", "L_"])
  
          # Based on Algorithm 3.2 of GPML
          K_star = self.kernel_(self.X_train_, X)  # K_star =k(x_star)
          f_star = K_star.T.dot(self.y_train_ - self.pi_)  # Line 4
          v = solve(self.L_, self.W_sr_[:, np.newaxis] * K_star)  # Line 5
          # Line 6 (compute np.diag(v.T.dot(v)) via einsum)
          var_f_star = self.kernel_.diag(X) - np.einsum("ij,ij->j", v, v)
  
          # Line 7:
          # Approximate \int log(z) * N(z | f_star, var_f_star)
          # Approximation is due to Williams & Barber, "Bayesian Classification
          # with Gaussian Processes", Appendix A: Approximate the logistic
          # sigmoid by a linear combination of 5 error functions.
          # For information on how this integral can be computed see
          # blitiri.blogspot.de/2012/11/gaussian-integral-of-error-function.html
          alpha = 1 / (2 * var_f_star)
          gamma = LAMBDAS * f_star
          integrals = np.sqrt(np.pi / alpha) \
              * erf(gamma * np.sqrt(alpha / (alpha + LAMBDAS**2))) \
              / (2 * np.sqrt(var_f_star * 2 * np.pi))
          pi_star = (COEFS * integrals).sum(axis=0) + .5 * COEFS.sum()
  
          return np.vstack((1 - pi_star, pi_star)).T
  
      def log_marginal_likelihood(self, theta=None, eval_gradient=False):
          """Returns log-marginal likelihood of theta for training data.
  
          Parameters
          ----------
          theta : array-like, shape = (n_kernel_params,) or None
              Kernel hyperparameters for which the log-marginal likelihood is
              evaluated. 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. 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.
          """
          if theta is None:
              if eval_gradient:
                  raise ValueError(
                      "Gradient can only be evaluated for theta!=None")
              return self.log_marginal_likelihood_value_
  
          kernel = self.kernel_.clone_with_theta(theta)
  
          if eval_gradient:
              K, K_gradient = kernel(self.X_train_, eval_gradient=True)
          else:
              K = kernel(self.X_train_)
  
          # Compute log-marginal-likelihood Z and also store some temporaries
          # which can be reused for computing Z's gradient
          Z, (pi, W_sr, L, b, a) = \
              self._posterior_mode(K, return_temporaries=True)
  
          if not eval_gradient:
              return Z
  
          # Compute gradient based on Algorithm 5.1 of GPML
          d_Z = np.empty(theta.shape[0])
          # XXX: Get rid of the np.diag() in the next line
          R = W_sr[:, np.newaxis] * cho_solve((L, True), np.diag(W_sr))  # Line 7
          C = solve(L, W_sr[:, np.newaxis] * K)  # Line 8
          # Line 9: (use einsum to compute np.diag(C.T.dot(C))))
          s_2 = -0.5 * (np.diag(K) - np.einsum('ij, ij -> j', C, C)) \
              * (pi * (1 - pi) * (1 - 2 * pi))  # third derivative
  
          for j in range(d_Z.shape[0]):
              C = K_gradient[:, :, j]   # Line 11
              # Line 12: (R.T.ravel().dot(C.ravel()) = np.trace(R.dot(C)))
              s_1 = .5 * a.T.dot(C).dot(a) - .5 * R.T.ravel().dot(C.ravel())
  
              b = C.dot(self.y_train_ - pi)  # Line 13
              s_3 = b - K.dot(R.dot(b))  # Line 14
  
              d_Z[j] = s_1 + s_2.T.dot(s_3)  # Line 15
  
          return Z, d_Z
  
      def _posterior_mode(self, K, return_temporaries=False):
          """Mode-finding for binary Laplace GPC and fixed kernel.
  
          This approximates the posterior of the latent function values for given
          inputs and target observations with a Gaussian approximation and uses
          Newton's iteration to find the mode of this approximation.
          """
          # Based on Algorithm 3.1 of GPML
  
          # If warm_start are enabled, we reuse the last solution for the
          # posterior mode as initialization; otherwise, we initialize with 0
          if self.warm_start and hasattr(self, "f_cached") \
             and self.f_cached.shape == self.y_train_.shape:
              f = self.f_cached
          else:
              f = np.zeros_like(self.y_train_, dtype=np.float64)
  
          # Use Newton's iteration method to find mode of Laplace approximation
          log_marginal_likelihood = -np.inf
          for _ in range(self.max_iter_predict):
              # Line 4
              pi = 1 / (1 + np.exp(-f))
              W = pi * (1 - pi)
              # Line 5
              W_sr = np.sqrt(W)
              W_sr_K = W_sr[:, np.newaxis] * K
              B = np.eye(W.shape[0]) + W_sr_K * W_sr
              L = cholesky(B, lower=True)
              # Line 6
              b = W * f + (self.y_train_ - pi)
              # Line 7
              a = b - W_sr * cho_solve((L, True), W_sr_K.dot(b))
              # Line 8
              f = K.dot(a)
  
              # Line 10: Compute log marginal likelihood in loop and use as
              #          convergence criterion
              lml = -0.5 * a.T.dot(f) \
                  - np.log(1 + np.exp(-(self.y_train_ * 2 - 1) * f)).sum() \
                  - np.log(np.diag(L)).sum()
              # Check if we have converged (log marginal likelihood does
              # not decrease)
              # XXX: more complex convergence criterion
              if lml - log_marginal_likelihood < 1e-10:
                  break
              log_marginal_likelihood = lml
  
          self.f_cached = f  # Remember solution for later warm-starts
          if return_temporaries:
              return log_marginal_likelihood, (pi, W_sr, L, b, a)
          else:
              return log_marginal_likelihood
  
      def _constrained_optimization(self, obj_func, initial_theta, bounds):
          if self.optimizer == "fmin_l_bfgs_b":
              theta_opt, func_min, convergence_dict = \
                  fmin_l_bfgs_b(obj_func, initial_theta, bounds=bounds)
              if convergence_dict["warnflag"] != 0:
                  warnings.warn("fmin_l_bfgs_b terminated abnormally with the "
                                " state: %s" % convergence_dict)
          elif callable(self.optimizer):
              theta_opt, func_min = \
                  self.optimizer(obj_func, initial_theta, bounds=bounds)
          else:
              raise ValueError("Unknown optimizer %s." % self.optimizer)
  
          return theta_opt, func_min
  
  
  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-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]))
  