# `sklearn.decomposition`.DictionaryLearning¶

class `sklearn.decomposition.``DictionaryLearning`(n_components=None, alpha=1, max_iter=1000, tol=1e-08, fit_algorithm=’lars’, transform_algorithm=’omp’, transform_n_nonzero_coefs=None, transform_alpha=None, n_jobs=1, code_init=None, dict_init=None, verbose=False, split_sign=False, random_state=None)[source]

Dictionary learning

Finds a dictionary (a set of atoms) that can best be used to represent data using a sparse code.

Solves the optimization problem:

```(U^*,V^*) = argmin 0.5 || Y - U V ||_2^2 + alpha * || U ||_1
(U,V)
with || V_k ||_2 = 1 for all  0 <= k < n_components
```

Read more in the User Guide.

Parameters: n_components : int, number of dictionary elements to extract alpha : float, sparsity controlling parameter max_iter : int, maximum number of iterations to perform tol : float, tolerance for numerical error fit_algorithm : {‘lars’, ‘cd’} lars: uses the least angle regression method to solve the lasso problem (linear_model.lars_path) cd: uses the coordinate descent method to compute the Lasso solution (linear_model.Lasso). Lars will be faster if the estimated components are sparse. New in version 0.17: cd coordinate descent method to improve speed. transform_algorithm : {‘lasso_lars’, ‘lasso_cd’, ‘lars’, ‘omp’, ‘threshold’} Algorithm used to transform the data lars: uses the least angle regression method (linear_model.lars_path) lasso_lars: uses Lars to compute the Lasso solution lasso_cd: uses the coordinate descent method to compute the Lasso solution (linear_model.Lasso). lasso_lars will be faster if the estimated components are sparse. omp: uses orthogonal matching pursuit to estimate the sparse solution threshold: squashes to zero all coefficients less than alpha from the projection `dictionary * X'` New in version 0.17: lasso_cd coordinate descent method to improve speed. transform_n_nonzero_coefs : int, `0.1 * n_features` by default Number of nonzero coefficients to target in each column of the solution. This is only used by algorithm=’lars’ and algorithm=’omp’ and is overridden by alpha in the omp case. transform_alpha : float, 1. by default If algorithm=’lasso_lars’ or algorithm=’lasso_cd’, alpha is the penalty applied to the L1 norm. If algorithm=’threshold’, alpha is the absolute value of the threshold below which coefficients will be squashed to zero. If algorithm=’omp’, alpha is the tolerance parameter: the value of the reconstruction error targeted. In this case, it overrides n_nonzero_coefs. n_jobs : int, number of parallel jobs to run code_init : array of shape (n_samples, n_components), initial value for the code, for warm restart dict_init : array of shape (n_components, n_features), initial values for the dictionary, for warm restart verbose : bool, optional (default: False) To control the verbosity of the procedure. split_sign : bool, False by default Whether to split the sparse feature vector into the concatenation of its negative part and its positive part. This can improve the performance of downstream classifiers. random_state : int, RandomState instance or None, optional (default=None) If int, random_state is the seed used by the random number generator; If RandomState instance, random_state is the random number generator; If None, the random number generator is the RandomState instance used by np.random. components_ : array, [n_components, n_features] dictionary atoms extracted from the data error_ : array vector of errors at each iteration n_iter_ : int Number of iterations run.

Notes

References:

J. Mairal, F. Bach, J. Ponce, G. Sapiro, 2009: Online dictionary learning for sparse coding (http://www.di.ens.fr/sierra/pdfs/icml09.pdf)

Methods

 `fit`(X[, y]) Fit the model from data in X. `fit_transform`(X[, y]) Fit to data, then transform it. `get_params`([deep]) Get parameters for this estimator. `set_params`(**params) Set the parameters of this estimator. `transform`(X) Encode the data as a sparse combination of the dictionary atoms.
`__init__`(n_components=None, alpha=1, max_iter=1000, tol=1e-08, fit_algorithm=’lars’, transform_algorithm=’omp’, transform_n_nonzero_coefs=None, transform_alpha=None, n_jobs=1, code_init=None, dict_init=None, verbose=False, split_sign=False, random_state=None)[source]
`fit`(X, y=None)[source]

Fit the model from data in X.

Parameters: X : array-like, shape (n_samples, n_features) Training vector, where n_samples in the number of samples and n_features is the number of features. y : Ignored. self : object Returns the object itself
`fit_transform`(X, y=None, **fit_params)[source]

Fit to data, then transform it.

Fits transformer to X and y with optional parameters fit_params and returns a transformed version of X.

Parameters: X : numpy array of shape [n_samples, n_features] Training set. y : numpy array of shape [n_samples] Target values. X_new : numpy array of shape [n_samples, n_features_new] Transformed array.
`get_params`(deep=True)[source]

Get parameters for this estimator.

Parameters: deep : boolean, optional If True, will return the parameters for this estimator and contained subobjects that are estimators. params : mapping of string to any Parameter names mapped to their values.
`set_params`(**params)[source]

Set the parameters of this estimator.

The method works on simple estimators as well as on nested objects (such as pipelines). The latter have parameters of the form `<component>__<parameter>` so that it’s possible to update each component of a nested object.

Returns: self :
`transform`(X)[source]

Encode the data as a sparse combination of the dictionary atoms.

Coding method is determined by the object parameter transform_algorithm.

Parameters: X : array of shape (n_samples, n_features) Test data to be transformed, must have the same number of features as the data used to train the model. X_new : array, shape (n_samples, n_components) Transformed data