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Multi-layer Perceptron classifier.
This model optimizes the log-loss function using LBFGS or stochastic gradient descent.
Added in version 0.18.
The ith element represents the number of neurons in the ith hidden layer.
Activation function for the hidden layer.
‘identity’, no-op activation, useful to implement linear bottleneck, returns f(x) = x
‘logistic’, the logistic sigmoid function, returns f(x) = 1 / (1 + exp(-x)).
‘tanh’, the hyperbolic tan function, returns f(x) = tanh(x).
‘relu’, the rectified linear unit function, returns f(x) = max(0, x)
The solver for weight optimization.
‘lbfgs’ is an optimizer in the family of quasi-Newton methods.
‘sgd’ refers to stochastic gradient descent.
‘adam’ refers to a stochastic gradient-based optimizer proposed by Kingma, Diederik, and Jimmy Ba
For a comparison between Adam optimizer and SGD, see Compare Stochastic learning strategies for MLPClassifier .
Note: The default solver ‘adam’ works pretty well on relatively large datasets (with thousands of training samples or more) in terms of both training time and validation score. For small datasets, however, ‘lbfgs’ can converge faster and perform better.
Strength of the L2 regularization term. The L2 regularization term is divided by the sample size when added to the loss.
For an example usage and visualization of varying regularization, see Varying regularization in Multi-layer Perceptron .
Size of minibatches for stochastic optimizers.
If the solver is ‘lbfgs’, the classifier will not use minibatch.
When set to “auto”,
batch_size=min(200,
n_samples)
.
Learning rate schedule for weight updates.
‘constant’ is a constant learning rate given by ‘learning_rate_init’.
‘invscaling’ gradually decreases the learning rate at each time step ‘t’ using an inverse scaling exponent of ‘power_t’. effective_learning_rate = learning_rate_init / pow(t, power_t)
‘adaptive’ keeps the learning rate constant to ‘learning_rate_init’ as long as training loss keeps decreasing. Each time two consecutive epochs fail to decrease training loss by at least tol, or fail to increase validation score by at least tol if ‘early_stopping’ is on, the current learning rate is divided by 5.
Only used when
solver='sgd'
.
The initial learning rate used. It controls the step-size in updating the weights. Only used when solver=’sgd’ or ‘adam’.
The exponent for inverse scaling learning rate. It is used in updating effective learning rate when the learning_rate is set to ‘invscaling’. Only used when solver=’sgd’.
Maximum number of iterations. The solver iterates until convergence (determined by ‘tol’) or this number of iterations. For stochastic solvers (‘sgd’, ‘adam’), note that this determines the number of epochs (how many times each data point will be used), not the number of gradient steps.
Whether to shuffle samples in each iteration. Only used when solver=’sgd’ or ‘adam’.
Determines random number generation for weights and bias initialization, train-test split if early stopping is used, and batch sampling when solver=’sgd’ or ‘adam’. Pass an int for reproducible results across multiple function calls. See Glossary .
Tolerance for the optimization. When the loss or score is not improving
by at least
tol
for
n_iter_no_change
consecutive iterations,
unless
learning_rate
is set to ‘adaptive’, convergence is
considered to be reached and training stops.
Whether to print progress messages to stdout.
When set to True, reuse the solution of the previous call to fit as initialization, otherwise, just erase the previous solution. See the Glossary .
Momentum for gradient descent update. Should be between 0 and 1. Only used when solver=’sgd’.
Whether to use Nesterov’s momentum. Only used when solver=’sgd’ and momentum > 0.
Whether to use early stopping to terminate training when validation
score is not improving. If set to true, it will automatically set
aside 10% of training data as validation and terminate training when
validation score is not improving by at least
tol
for
n_iter_no_change
consecutive epochs. The split is stratified,
except in a multilabel setting.
If early stopping is False, then the training stops when the training
loss does not improve by more than tol for n_iter_no_change consecutive
passes over the training set.
Only effective when solver=’sgd’ or ‘adam’.
The proportion of training data to set aside as validation set for early stopping. Must be between 0 and 1. Only used if early_stopping is True.
Exponential decay rate for estimates of first moment vector in adam, should be in [0, 1). Only used when solver=’adam’.
Exponential decay rate for estimates of second moment vector in adam, should be in [0, 1). Only used when solver=’adam’.
Value for numerical stability in adam. Only used when solver=’adam’.
Maximum number of epochs to not meet
tol
improvement.
Only effective when solver=’sgd’ or ‘adam’.
Added in version 0.20.
Only used when solver=’lbfgs’. Maximum number of loss function calls.
The solver iterates until convergence (determined by ‘tol’), number
of iterations reaches max_iter, or this number of loss function calls.
Note that number of loss function calls will be greater than or equal
to the number of iterations for the
MLPClassifier
.
Added in version 0.22.
Class labels for each output.
The current loss computed with the loss function.
The minimum loss reached by the solver throughout fitting.
If
early_stopping=True
, this attribute is set to
None
. Refer to
the
best_validation_score_
fitted attribute instead.
n_iter_
,)
The ith element in the list represents the loss at the ith iteration.
n_iter_
,) or None
The score at each iteration on a held-out validation set. The score
reported is the accuracy score. Only available if
early_stopping=True
,
otherwise the attribute is set to
None
.
The best validation score (i.e. accuracy score) that triggered the
early stopping. Only available if
early_stopping=True
, otherwise the
attribute is set to
None
.
The number of training samples seen by the solver during fitting.
The ith element in the list represents the weight matrix corresponding to layer i.
The ith element in the list represents the bias vector corresponding to layer i + 1.
Number of features seen during fit .
Added in version 0.24.
n_features_in_
,)
Names of features seen during
fit
. Defined only when
X
has feature names that are all strings.
Added in version 1.0.
The number of iterations the solver has run.
Number of layers.
Number of outputs.
Name of the output activation function.
Notes
MLPClassifier trains iteratively since at each time step the partial derivatives of the loss function with respect to the model parameters are computed to update the parameters.
It can also have a regularization term added to the loss function that shrinks model parameters to prevent overfitting.
This implementation works with data represented as dense numpy arrays or sparse scipy arrays of floating point values.
References
Hinton, Geoffrey E. “Connectionist learning procedures.” Artificial intelligence 40.1 (1989): 185-234.
Glorot, Xavier, and Yoshua Bengio. “Understanding the difficulty of training deep feedforward neural networks.” International Conference on Artificial Intelligence and Statistics. 2010.
Kingma, Diederik, and Jimmy Ba (2014) “Adam: A method for stochastic optimization.”
Examples
>>> from sklearn.neural_network import MLPClassifier
>>> from sklearn.datasets import make_classification
>>> from sklearn.model_selection import train_test_split
>>> X, y = make_classification(n_samples=100, random_state=1)
>>> X_train, X_test, y_train, y_test = train_test_split(X, y, stratify=y,
... random_state=1)
>>> clf = MLPClassifier(random_state=1, max_iter=300).fit(X_train, y_train)
>>> clf.predict_proba(X_test[:1])
array([[0.0383, 0.961]])
>>> clf.predict(X_test[:5, :])
array([1, 0, 1, 0, 1])
>>> clf.score(X_test, y_test)
0.8...
fit(X, y, sample_weight=None)[source]#
Fit the model to data matrix X and target(s) y.
Parameters:
Xndarray or sparse matrix of shape (n_samples, n_features) The input data.
yndarray of shape (n_samples,) or (n_samples, n_outputs) The target values (class labels in classification, real numbers in
regression).
sample_weightarray-like of shape (n_samples,), default=None Sample weights.
Added in version 1.7.
get_metadata_routing()[source]#
Get metadata routing of this object.
Please check User Guide on how the routing
mechanism works.
Returns:
routingMetadataRequest A MetadataRequest encapsulating
routing information.
Parameters:
deepbool, default=True If True, will return the parameters for this estimator and
contained subobjects that are estimators.
Returns:
paramsdict Parameter names mapped to their values.
partial_fit(X, y, sample_weight=None, classes=None)[source]#
Update the model with a single iteration over the given data.
Parameters:
X{array-like, sparse matrix} of shape (n_samples, n_features) The input data.
yarray-like of shape (n_samples,) The target values.
sample_weightarray-like of shape (n_samples,), default=None Sample weights.
Added in version 1.7.
classesarray of shape (n_classes,), default=None Classes across all calls to partial_fit.
Can be obtained via np.unique(y_all), where y_all is the
target vector of the entire dataset.
This argument is required for the first call to partial_fit
and can be omitted in the subsequent calls.
Note that y doesn’t need to contain all labels in classes.
Returns:
selfobject Trained MLP model.
Returns:
log_y_probndarray of shape (n_samples, n_classes) The predicted log-probability of the sample for each class
in the model, where classes are ordered as they are in
self.classes_. Equivalent to log(predict_proba(X)).
Returns:
y_probndarray of shape (n_samples, n_classes)
The predicted probability of the sample for each class in the
model, where classes are ordered as they are in self.classes_.
score(X, y, sample_weight=None)[source]#
Return accuracy on provided data and labels.
In multi-label classification, this is the subset accuracy
which is a harsh metric since you require for each sample that
each label set be correctly predicted.
Parameters:
Xarray-like of shape (n_samples, n_features) Test samples.
yarray-like of shape (n_samples,) or (n_samples, n_outputs) True labels for X.
sample_weightarray-like of shape (n_samples,), default=None Sample weights.
Returns:
scorefloat Mean accuracy of self.predict(X) w.r.t. y.
set_fit_request(*, sample_weight: bool | None | str = '$UNCHANGED$') → MLPClassifier[source]#
Configure whether metadata should be requested to be passed to the fit method.
Note that this method is only relevant when this estimator is used as a
sub-estimator within a meta-estimator and metadata routing is enabled
with enable_metadata_routing=True (see sklearn.set_config).
Please check the User Guide on how the routing
mechanism works.
The options for each parameter are:
True: metadata is requested, and passed to fit if provided. The request is ignored if metadata is not provided.
False: metadata is not requested and the meta-estimator will not pass it to fit.
None: metadata is not requested, and the meta-estimator will raise an error if the user provides it.
str: metadata should be passed to the meta-estimator with this given alias instead of the original name.
The default (sklearn.utils.metadata_routing.UNCHANGED) retains the
existing request. This allows you to change the request for some
parameters and not others.
Added in version 1.3.
Parameters:
sample_weightstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED Metadata routing for sample_weight parameter in fit.
Returns:
selfobject The updated object.
set_params(**params)[source]#
Set the parameters of this estimator.
The method works on simple estimators as well as on nested objects
(such as Pipeline). The latter have
parameters of the form <component>__<parameter> so that it’s
possible to update each component of a nested object.
Parameters:
**paramsdict Estimator parameters.
Returns:
selfestimator instance Estimator instance.
set_partial_fit_request(*, classes: bool | None | str = '$UNCHANGED$', sample_weight: bool | None | str = '$UNCHANGED$') → MLPClassifier[source]#
Configure whether metadata should be requested to be passed to the partial_fit method.
Note that this method is only relevant when this estimator is used as a
sub-estimator within a meta-estimator and metadata routing is enabled
with enable_metadata_routing=True (see sklearn.set_config).
Please check the User Guide on how the routing
mechanism works.
The options for each parameter are:
True: metadata is requested, and passed to partial_fit if provided. The request is ignored if metadata is not provided.
False: metadata is not requested and the meta-estimator will not pass it to partial_fit.
None: metadata is not requested, and the meta-estimator will raise an error if the user provides it.
str: metadata should be passed to the meta-estimator with this given alias instead of the original name.
The default (sklearn.utils.metadata_routing.UNCHANGED) retains the
existing request. This allows you to change the request for some
parameters and not others.
Added in version 1.3.
Parameters:
classesstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED Metadata routing for classes parameter in partial_fit.
sample_weightstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED Metadata routing for sample_weight parameter in partial_fit.
Returns:
selfobject The updated object.
set_score_request(*, sample_weight: bool | None | str = '$UNCHANGED$') → MLPClassifier[source]#
Configure whether metadata should be requested to be passed to the score method.
Note that this method is only relevant when this estimator is used as a
sub-estimator within a meta-estimator and metadata routing is enabled
with enable_metadata_routing=True (see sklearn.set_config).
Please check the User Guide on how the routing
mechanism works.
The options for each parameter are:
True: metadata is requested, and passed to score if provided. The request is ignored if metadata is not provided.
False: metadata is not requested and the meta-estimator will not pass it to score.
None: metadata is not requested, and the meta-estimator will raise an error if the user provides it.
str: metadata should be passed to the meta-estimator with this given alias instead of the original name.
The default (sklearn.utils.metadata_routing.UNCHANGED) retains the
existing request. This allows you to change the request for some
parameters and not others.
Added in version 1.3.
Parameters:
sample_weightstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED Metadata routing for sample_weight parameter in score.
Returns:
selfobject The updated object.
Varying regularization in Multi-layer Perceptron
Varying regularization in Multi-layer Perceptron
Compare Stochastic learning strategies for MLPClassifier
Compare Stochastic learning strategies for MLPClassifier
Visualization of MLP weights on MNIST
Visualization of MLP weights on MNIST
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