/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   *  Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *   *  Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *
 *   *  Neither the name of the University of Southampton nor the names of its
 *      contributors may be used to endorse or promote products derived from this
 *      software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package no.uib.cipr.matrix;

import org.netlib.util.intW;

import com.github.fommil.netlib.LAPACK;

/**
 * Computes economy singular value decompositions. Uses DGESDD internally.
 */
public class EconomySVD {

        /**
         * Work array
         */
        private final double[] work;

        /**
         * Work array
         */
        private final int[] iwork;

        /**
         * Matrix dimension
         */
        private final int m, n;

        /**
         * The singular values
         */
        private final double[] S;

        /**
         * Singular vectors
         */
        private final DenseMatrix U, Vt;

        /**
         * Creates an empty SVD
         *
         * @param m
         *            Number of rows
         * @param n
         *            Number of columns
         */
        public EconomySVD(int m, int n) {
                this.m = m;
                this.n = n;

                // Allocate space for the decomposition
                S = new double[Math.min(m, n)];
                U = new DenseMatrix(Matrices.ld(m), Math.min(m, n));
                Vt = new DenseMatrix(Matrices.ld(Math.min(m, n)), n);

                // Find workspace requirements
                iwork = new int[8 * Math.min(m, n)];

                // Query optimal workspace
                final double[] worksize = new double[1];
                final intW info = new intW(0);
                LAPACK.getInstance().dgesdd(JobSVD.Part.netlib(), m, n, new double[0],
                                Matrices.ld(m), new double[0], new double[0], U.numRows,
                                new double[0], Vt.numRows, worksize, -1, iwork, info);

                // Allocate workspace
                int lwork = -1;
                if (info.val != 0) {
                        // 'S' => LWORK >= min(M,N)*(6+4*min(M,N))+max(M,N)
                        lwork = Math.min(m, n) * (6 + 4 * Math.min(m, n)) + Math.max(m, n);
                } else
                        lwork = (int) worksize[0];

                lwork = Math.max(lwork, 1);
                work = new double[lwork];
        }

        /**
         * Convenience method for computing a full SVD
         *
         * @param A
         *            Matrix to decompose, not modified
         * @return Newly allocated factorization
         * @throws NotConvergedException
         */
        public static EconomySVD factorize(Matrix A) throws NotConvergedException {
                return new EconomySVD(A.numRows(), A.numColumns()).factor(new DenseMatrix(A));
        }

        /**
         * Computes an SVD
         *
         * @param A
         *            Matrix to decompose. Size must conform, and it will be
         *            overwritten on return. Pass a copy to avoid this
         * @return The current decomposition
         * @throws NotConvergedException
         */
        public EconomySVD factor(DenseMatrix A) throws NotConvergedException {
                if (A.numRows() != m)
                        throw new IllegalArgumentException("A.numRows() != m");
                else if (A.numColumns() != n)
                        throw new IllegalArgumentException("A.numColumns() != n");

                final intW info = new intW(0);

                LAPACK.getInstance().dgesdd(JobSVD.Part.netlib(), m, n,
                                A.getData(), A.numRows,
                                S,
                                U.getData(), U.numRows,
                                Vt.getData(), Vt.numRows,
                                work, work.length, iwork, info);

                if (info.val > 0)
                        throw new NotConvergedException(
                                        NotConvergedException.Reason.Iterations);
                else if (info.val < 0)
                        throw new IllegalArgumentException();

                return this;
        }

        /**
         * Returns the left singular vectors, column-wise. Not available for partial
         * decompositions
         *
         * @return Matrix of size m*m
         */
        public DenseMatrix getU() {
                return U;
        }

        /**
         * Returns the right singular vectors, row-wise. Not available for partial
         * decompositions
         *
         * @return Matrix of size n*n
         */
        public DenseMatrix getVt() {
                return Vt;
        }

        /**
         * Returns the singular values (stored in descending order)
         *
         * @return Array of size min(m,n)
         */
        public double[] getS() {
                return S;
        }

}