001/*******************************************************************************
002 * This software is provided as a supplement to the authors' textbooks on digital
003 * image processing published by Springer-Verlag in various languages and editions.
004 * Permission to use and distribute this software is granted under the BSD 2-Clause
005 * "Simplified" License (see http://opensource.org/licenses/BSD-2-Clause).
006 * Copyright (c) 2006-2023 Wilhelm Burger, Mark J. Burge. All rights reserved.
007 * Visit https://imagingbook.com for additional details.
008 ******************************************************************************/
009package imagingbook.common.math.eigen;
010
011import org.apache.commons.math3.linear.EigenDecomposition;
012import org.apache.commons.math3.linear.RealMatrix;
013import org.apache.commons.math3.linear.RealVector;
014
015/**
016 * An implementation of {@link RealEigenDecomposition}, which merely wraps an instance of {@link EigenDecomposition} as
017 * provided by the Apache Commons Math library. Note this works only for square matrices and symmetry and zero
018 * tolerances cannot be specified, default values are always used. The Jama version ({@link EigenDecompositionJama})
019 * generally appears to be more flexible and robust.
020 *
021 * @author WB
022 * @version 2022/11/24
023 * @see EigenDecompositionJama
024 * @see Eigensolver2x2
025 */
026public class EigenDecompositionApache implements RealEigenDecomposition {
027        
028        // instance of org.apache.commons.math3.linear.EigenDecomposition
029        private final EigenDecomposition decomp;
030
031        /**
032         * Constructor, calculates the eigen decomposition of the specified matrix, which must be square but does not need
033         * to be symmetric.
034         *
035         * @param M the matrix to decompose
036         */
037        public EigenDecompositionApache(RealMatrix M) {
038                this.decomp = new EigenDecomposition(M);
039        }
040
041        @Override
042        public boolean hasComplexEigenvalues() {
043                return decomp.hasComplexEigenvalues();
044        }
045
046        @Override
047        public double getRealEigenvalue(int k) {
048                return decomp.getRealEigenvalue(k);
049        }
050
051        @Override
052        public double[] getRealEigenvalues() {
053                return decomp.getRealEigenvalues();
054        }
055
056        @Override
057        public RealVector getEigenvector(int k) {
058                return decomp.getEigenvector(k);
059        }
060
061        @Override
062        public RealMatrix getV() {
063                return decomp.getV();
064        }
065
066        /**
067         * Returns the underlying Apache eigendecomposition instance, mainly for debugging.
068         *
069         * @return the Apache eigendecomposition instance
070         */
071        public EigenDecomposition getInternalDecomposition() {
072                return decomp;
073        }
074
075}