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/**
 * 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
        double[] worksize = new double[1];
        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");
        }

        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;
    }
}