test_isomap.py 文件源码

def test_isomap_reconstruction_error():
    # Same setup as in test_isomap_simple_grid, with an added dimension
    N_per_side = 5
    Npts = N_per_side ** 2
    n_neighbors = Npts - 1

    # grid of equidistant points in 2D, n_components = n_dim
    X = np.array(list(product(range(N_per_side), repeat=2)))

    # add noise in a third dimension
    rng = np.random.RandomState(0)
    noise = 0.1 * rng.randn(Npts, 1)
    X = np.concatenate((X, noise), 1)

    # compute input kernel
    G = neighbors.kneighbors_graph(X, n_neighbors,
                                   mode='distance').toarray()

    centerer = preprocessing.KernelCenterer()
    K = centerer.fit_transform(-0.5 * G ** 2)

    for eigen_solver in eigen_solvers:
        for path_method in path_methods:
            clf = manifold.Isomap(n_neighbors=n_neighbors, n_components=2,
                                  eigen_solver=eigen_solver,
                                  path_method=path_method)
            clf.fit(X)

            # compute output kernel
            G_iso = neighbors.kneighbors_graph(clf.embedding_,
                                               n_neighbors,
                                               mode='distance').toarray()

            K_iso = centerer.fit_transform(-0.5 * G_iso ** 2)

            # make sure error agrees
            reconstruction_error = np.linalg.norm(K - K_iso) / Npts
            assert_almost_equal(reconstruction_error,
                                clf.reconstruction_error())