sklearn.linear_model.orthogonal_mp_gram¶
- sklearn.linear_model.orthogonal_mp_gram(Gram, Xy, n_nonzero_coefs=None, tol=None, norms_squared=None, copy_Gram=True, copy_Xy=True, return_path=False)¶
Gram Orthogonal Matching Pursuit (OMP)
Solves n_targets Orthogonal Matching Pursuit problems using only the Gram matrix X.T * X and the product X.T * y.
Parameters : Gram: array, shape (n_features, n_features) :
Gram matrix of the input data: X.T * X
Xy: array, shape (n_features,) or (n_features, n_targets) :
Input targets multiplied by X: X.T * y
n_nonzero_coefs: int :
Desired number of non-zero entries in the solution. If None (by default) this value is set to 10% of n_features.
tol: float :
Maximum norm of the residual. If not None, overrides n_nonzero_coefs.
norms_squared: array-like, shape (n_targets,) :
Squared L2 norms of the lines of y. Required if tol is not None.
copy_Gram: bool, optional :
Whether the gram matrix must be copied by the algorithm. A false value is only helpful if it is already Fortran-ordered, otherwise a copy is made anyway.
copy_Xy: bool, optional :
Whether the covariance vector Xy must be copied by the algorithm. If False, it may be overwritten.
return_path: bool, optional. Default: False :
Whether to return every value of the nonzero coefficients along the forward path. Useful for cross-validation.
Returns : coef: array, shape (n_features,) or (n_features, n_targets) :
Coefficients of the OMP solution. If return_path=True, this contains the whole coefficient path. In this case its shape is (n_features, n_features) or (n_features, n_targets, n_features) and iterating over the last axis yields coefficients in increasing order of active features.
See also
OrthogonalMatchingPursuit, orthogonal_mp, lars_path, decomposition.sparse_encode
Notes
Orthogonal matching pursuit was introduced in G. Mallat, Z. Zhang, Matching pursuits with time-frequency dictionaries, IEEE Transactions on Signal Processing, Vol. 41, No. 12. (December 1993), pp. 3397-3415. (http://blanche.polytechnique.fr/~mallat/papiers/MallatPursuit93.pdf)
This implementation is based on Rubinstein, R., Zibulevsky, M. and Elad, M., Efficient Implementation of the K-SVD Algorithm using Batch Orthogonal Matching Pursuit Technical Report - CS Technion, April 2008. http://www.cs.technion.ac.il/~ronrubin/Publications/KSVD-OMP-v2.pdf