dasf.ml.cluster.spectral

Spectral Clustering algorithm module.

Classes

SpectralClustering

Apply clustering to a projection of the normalized Laplacian.

Module Contents

class dasf.ml.cluster.spectral.SpectralClustering(n_clusters=8, eigen_solver=None, random_state=None, n_init=10, gamma=1.0, affinity='rbf', n_neighbors=10, eigen_tol=0.0, assign_labels='kmeans', degree=3, coef0=1, kernel_params=None, n_jobs=None, n_components=None, persist_embedding=False, kmeans_params=None, verbose=False, **kwargs)

Bases: dasf.ml.cluster.classifier.ClusterClassifier

Apply clustering to a projection of the normalized Laplacian.

In practice Spectral Clustering is very useful when the structure of the individual clusters is highly non-convex, or more generally when a measure of the center and spread of the cluster is not a suitable description of the complete cluster, such as when clusters are nested circles on the 2D plane.

If the affinity matrix is the adjacency matrix of a graph, this method can be used to find normalized graph cuts.

When calling fit, an affinity matrix is constructed using either a kernel function such the Gaussian (aka RBF) kernel with Euclidean distance d(X, X):

np.exp(-gamma * d(X,X) ** 2)

or a k-nearest neighbors connectivity matrix.

Alternatively, a user-provided affinity matrix can be specified by setting affinity='precomputed'.

Read more in the User Guide.

Parameters

n_clustersint, default=8

The dimension of the projection subspace.

eigen_solver{‘arpack’, ‘lobpcg’, ‘amg’}, default=None

The eigenvalue decomposition strategy to use. AMG requires pyamg to be installed. It can be faster on very large, sparse problems, but may also lead to instabilities. If None, then 'arpack' is used.

n_componentsint, default=n_clusters

Number of eigenvectors to use for the spectral embedding

random_stateint, RandomState instance, default=None

A pseudo random number generator used for the initialization of the lobpcg eigenvectors decomposition when eigen_solver='amg' and by the K-Means initialization. Use an int to make the randomness deterministic. See Glossary.

n_initint, default=10

Number of time the k-means algorithm will be run with different centroid seeds. The final results will be the best output of n_init consecutive runs in terms of inertia. Only used if assign_labels='kmeans'.

gammafloat, default=1.0

Kernel coefficient for rbf, poly, sigmoid, laplacian and chi2 kernels. Ignored for affinity='nearest_neighbors'.

affinitystr or callable, default=’rbf’
How to construct the affinity matrix.

  • ‘nearest_neighbors’: construct the affinity matrix by computing a graph of nearest neighbors.

  • ‘rbf’: construct the affinity matrix using a radial basis function (RBF) kernel.

  • ‘precomputed’: interpret X as a precomputed affinity matrix, where larger values indicate greater similarity between instances.

  • ‘precomputed_nearest_neighbors’: interpret X as a sparse graph of precomputed distances, and construct a binary affinity matrix from the n_neighbors nearest neighbors of each instance.

  • one of the kernels supported by pairwise_kernels().

Only kernels that produce similarity scores (non-negative values that increase with similarity) should be used. This property is not checked by the clustering algorithm.

n_neighborsint, default=10

Number of neighbors to use when constructing the affinity matrix using the nearest neighbors method. Ignored for affinity='rbf'.

eigen_tolfloat, default=0.0

Stopping criterion for eigendecomposition of the Laplacian matrix when eigen_solver='arpack'.

assign_labels{‘kmeans’, ‘discretize’}, default=’kmeans’

The strategy for assigning labels in the embedding space. There are two ways to assign labels after the Laplacian embedding. k-means is a popular choice, but it can be sensitive to initialization. Discretization is another approach which is less sensitive to random initialization.

degreefloat, default=3

Degree of the polynomial kernel. Ignored by other kernels.

coef0float, default=1

Zero coefficient for polynomial and sigmoid kernels. Ignored by other kernels.

kernel_paramsdict of str to any, default=None

Parameters (keyword arguments) and values for kernel passed as callable object. Ignored by other kernels.

n_jobsint, default=None

The number of parallel jobs to run when affinity=’nearest_neighbors’ or affinity=’precomputed_nearest_neighbors’. The neighbors search will be done in parallel. None means 1 unless in a joblib.parallel_backend context. -1 means using all processors. See Glossary for more details.

verbosebool, default=False

Verbosity mode.

Added in version 0.24.

persist_embeddingbool

Whether to persist the intermediate n_samples x n_components array used for clustering.

kmeans_paramsdictionary of string to any, optional

Keyword arguments for the KMeans clustering used for the final clustering.

Examples

>>> from dasf.ml.cluster import SpectralClustering
>>> import numpy as np
>>> X = np.array([[1, 1], [2, 1], [1, 0],
...               [4, 7], [3, 5], [3, 6]])
>>> clustering = SpectralClustering(n_clusters=2,
...         assign_labels='discretize',
...         random_state=0).fit(X)
>>> clustering
SpectralClustering(assign_labels='discretize', n_clusters=2,
    random_state=0)

For further informations see: - https://scikit-learn.org/stable/modules/generated/sklearn.cluster.SpectralClustering.html#sklearn.cluster.SpectralClustering - https://ml.dask.org/modules/generated/dask_ml.cluster.SpectralClustering.html

Notes

A distance matrix for which 0 indicates identical elements and high values indicate very dissimilar elements can be transformed into an affinity / similarity matrix that is well-suited for the algorithm by applying the Gaussian (aka RBF, heat) kernel:

np.exp(- dist_matrix ** 2 / (2. * delta ** 2))

where delta is a free parameter representing the width of the Gaussian kernel.

An alternative is to take a symmetric version of the k-nearest neighbors connectivity matrix of the points.

If the pyamg package is installed, it is used: this greatly speeds up computation.

References

A generic constructor method.

_fit_cpu(X, y=None, sample_weight=None)

Perform spectral clustering from features, or affinity matrix using CPU only.

Parameters

X{array-like, sparse matrix} of shape (n_samples, n_features) or (n_samples, n_samples)

Training instances to cluster, similarities / affinities between instances if affinity='precomputed', or distances between instances if affinity='precomputed_nearest_neighbors. If a sparse matrix is provided in a format other than csr_matrix, csc_matrix, or coo_matrix, it will be converted into a sparse csr_matrix.

yIgnored

Not used, present here for API consistency by convention.

Returns

selfobject

A fitted instance of the estimator.

_lazy_fit_predict_cpu(X, y=None, sample_weight=None)

Perform spectral clustering on X and return cluster labels using Dask with CPU only.

Parameters

X{array-like, sparse matrix} of shape (n_samples, n_features) or (n_samples, n_samples)

Training instances to cluster, similarities / affinities between instances if affinity='precomputed', or distances between instances if affinity='precomputed_nearest_neighbors. If a sparse matrix is provided in a format other than csr_matrix, csc_matrix, or coo_matrix, it will be converted into a sparse csr_matrix.

yIgnored

Not used, present here for API consistency by convention.

Returns

labelsndarray of shape (n_samples,)

Cluster labels.

_fit_predict_cpu(X, y=None, sample_weight=None)

Perform spectral clustering on X and return cluster labels using CPU only.

Parameters

X{array-like, sparse matrix} of shape (n_samples, n_features) or (n_samples, n_samples)

Training instances to cluster, similarities / affinities between instances if affinity='precomputed', or distances between instances if affinity='precomputed_nearest_neighbors. If a sparse matrix is provided in a format other than csr_matrix, csc_matrix, or coo_matrix, it will be converted into a sparse csr_matrix.

yIgnored

Not used, present here for API consistency by convention.

Returns

labelsndarray of shape (n_samples,)

Cluster labels.