The spectral kernel machine combines kernel functions and spectral graph
theory for solving problems of machine learning. The data points in the
dataset are placed in the form of a matrix known as a kernel matrix, or
Gram matrix, containing all pairwise kernels between the data points. The
dataset is regarded as nodes of a fully connected graph. A weight equal
to the kernel between the two nodes is assigned to each edge of the
graph. The adjacency matrix of the graph is equivalent to the kernel
matrix, also known as the Gram matrix. The eigenvectors and their
corresponding eigenvalues provide information about the properties of the
graph, and thus, the dataset. The second eigenvector can be thresholded
to approximate the class assignment of graph nodes. Eigenvectors of the
kernel matrix may be used to assign unlabeled data to clusters, merge
information from labeled and unlabeled data by transduction, provide
model selection information for other kernels, detect novelties or
anomalies and/or clean data, and perform supervised learning tasks such
as classification.