ch.akuhn.matrix.eigenvalues.Eigenvalues Maven / Gradle / Ivy

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package ch.akuhn.matrix.eigenvalues;

import ch.akuhn.matrix.KuhnMatrix;
import ch.akuhn.matrix.Vector;

/**
 * The eigen-decomposition of a matrix.
 *
 * @author Adrian Kuhn
 */
public class Eigenvalues {

    /**
     * The eigenvalues
     */
    public double[] value;

    /**
     * The eigenvectors
     */
    public Vector[] vector;

    protected final int n;
    protected int nev;

    /**
     * Construct with the given dimensions
     *
     * @param n
     */
    public Eigenvalues(int n) {
        this.n = n;
        this.nev = n;
    }

    /**
     * Get an object that can compute the eigendecomposition of the given
     * matrix. If the matrix has fewer than 10 columns, this will be an
     * {@link AllEigenvalues}, otherwise it will be a {@link FewEigenvalues}.
     *
     * @param A
     * @return the object to compute the eigen decomposition
     */
    public static Eigenvalues of(KuhnMatrix A) {
        if (A.columnCount() == 0) {
            Eigenvalues eigen = new Eigenvalues(0);
            eigen.value = new double[0];
            eigen.vector = new Vector[0];
            return eigen;
        }
        if (A.columnCount() == 1) {
            Eigenvalues eigen = new Eigenvalues(0);
            eigen.value = new double[] { A.get(0, 0) };
            eigen.vector = new Vector[] { Vector.from(1.0) };
            return eigen;
        }
        if (A.columnCount() < 10) {
            return new AllEigenvalues(A);
        }
        return FewEigenvalues.of(A);
    }

    /**
     * Configure to compute the largest nev values/vectors.
     *
     * @param nev
     * @return this
     */
    public Eigenvalues largest(int nev) {
        this.nev = nev;
        return this;
    }

    /**
     * Run the decomposition algorithm. Subclasses should override as necessary.
     *
     * @return this
     */
    public Eigenvalues run() {
        return this;
    }

    /**
     * @return the total number of possible eigen vectors (i.e. the number of
     *         rows of the input)
     */
    public int getN() {
        return n;
    }
}