_make_nn_sparse_coded_signal.py

def _make_nn_sparse_coded_signal(n_samples, n_components, n_features,
                                 n_nonzero_coefs, random_state=None):
    """Generate a signal as a sparse combination of dictionary elements.
    Returns a matrix Y = DX, such as D is (n_features, n_components),
    X is (n_components, n_samples) and each column of X has exactly
    n_nonzero_coefs non-zero elements.
    Read more in the :ref:`User Guide <sample_generators>`.
    Parameters
    ----------
    n_samples : int
        number of samples to generate
    n_components :  int,
        number of components in the dictionary
    n_features : int
        number of features of the dataset to generate
    n_nonzero_coefs : int
        number of active (non-zero) coefficients in each sample
    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`.
    Returns
    -------
    data : array of shape [n_features, n_samples]
        The encoded signal (Y).
    dictionary : array of shape [n_features, n_components]
        The dictionary with normalized components (D).
    code : array of shape [n_components, n_samples]
        The sparse code such that each column of this matrix has exactly
        n_nonzero_coefs non-zero items (X).
    """
    generator = check_random_state(random_state)
    # generate dictionary
    D = abs(generator.randn(n_features, n_components))
    D /= np.sqrt(np.sum((D ** 2), axis=0))

    # generate code
    X = np.zeros((n_components, n_samples))
    for i in range(n_samples):
        idx = np.arange(n_components)
        generator.shuffle(idx)
        idx = idx[:n_nonzero_coefs]
        X[idx, i] = abs(generator.randn(n_nonzero_coefs))


    # encode signal
    Y = np.dot(D, X)

    return map(np.squeeze, (Y, D, X))