8.5.16. sklearn.decomposition.sparse_encode¶
- sklearn.decomposition.sparse_encode(X, dictionary, gram=None, cov=None, algorithm='lasso_lars', n_nonzero_coefs=None, alpha=None, copy_gram=True, copy_cov=True, init=None, max_iter=1000, n_jobs=1)¶
Sparse coding
Each row of the result is the solution to a sparse coding problem. The goal is to find a sparse array code such that:
X ~= code * dictionary
Parameters : X: array of shape (n_samples, n_features) :
Data matrix
dictionary: array of shape (n_atoms, n_features) :
The dictionary matrix against which to solve the sparse coding of the data. Some of the algorithms assume normalized rows for meaningful output.
gram: array, shape=(n_atoms, n_atoms) :
Precomputed Gram matrix, dictionary * dictionary’
cov: array, shape=(n_atoms, n_samples) :
Precomputed covariance, dictionary’ * X
algorithm: {‘lasso_lars’, ‘lasso_cd’, ‘lars’, ‘omp’, ‘threshold’} :
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’
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.
alpha: float, 1. by default :
If algorithm=’lasso_lars’ or algorithm=’lasso_cd’, alpha is the penalty applied to the L1 norm. If algorithm=’threhold’, 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.
init: array of shape (n_samples, n_atoms) :
Initialization value of the sparse codes. Only used if algorithm=’lasso_cd’.
max_iter: int, 1000 by default :
Maximum number of iterations to perform if algorithm=’lasso_cd’.
copy_gram: boolean, optional :
Whether to copy the precomputed Gram matrix; if False, it may be overwritten.
copy_cov: boolean, optional :
Whether to copy the precomputed covariance matrix; if False, it may be overwritten.
n_jobs: int, optional :
Number of parallel jobs to run.
Returns : code: array of shape (n_samples, n_atoms) :
The sparse codes