DiagonalMatrix.java

package sim.util.mantissa.linalg;

import java.io.Serializable;

/** This class implements diagonal matrices of linear algebra.

    <p>This file is from the "Mantissa" Java software package found at
    <a href="http://www.spaceroots.org/software/mantissa/index.html">
    http://www.spaceroots.org/software/mantissa/index.html</a>.  The license is included
    at the end of the source file.

    * @version $Id: DiagonalMatrix.java,v 1.1 2007-05-30 14:01:29 feijai Exp $
    * @author L. Maisonobe

    */

public class DiagonalMatrix
    extends SquareMatrix
    implements Serializable, Cloneable {
    /** Simple constructor.
     * This constructor builds a diagonal matrix of specified order, all
     * elements on the diagonal being ones (so this is an identity matrix).
     * @param order order of the matrix
     */
    public DiagonalMatrix(int order) {
        this(order, 1.0);
        }

    /** Simple constructor.
     * This constructor builds a diagonal matrix of specified order and
     * set all diagonal elements to the same value.
     * @param order order of the matrix
     * @param value value for the diagonal elements
     */
    public DiagonalMatrix(int order, double value) {
        super(order);
        for (int index = 0; index < order * order; index += order + 1) {
            data[index] = value;
            }
        }

    /** Simple constructor.
     * Build a matrix with specified elements.
     * @param order order of the matrix
     * @param data table of the matrix elements (stored row after row)
     */
    public DiagonalMatrix(int order, double[] data) {
        super(order, data);
        }

    /** Copy constructor.
     * @param d diagonal matrix to copy
     */
    public DiagonalMatrix(DiagonalMatrix d) {
        super(d);
        }

    public Matrix duplicate() {
        return new DiagonalMatrix(this);
        }

    public void setElement(int i, int j, double value) {
        if (i != j) {
            throw new ArrayIndexOutOfBoundsException("cannot set elements"
                + " out of diagonal in a"
                + " diagonal matrix");
            }
        super.setElement(i, j, value);
        }

    public double getDeterminant(double epsilon) {
        double determinant = data[0];
        for (int index = columns + 1; index < columns * columns; index += columns + 1) {
            determinant *= data[index];
            }
        return determinant;
        }

    public SquareMatrix getInverse(double epsilon)
        throws SingularMatrixException {

        DiagonalMatrix inv = new DiagonalMatrix (columns);

        for (int index = 0; index < columns * columns; index += columns + 1) {
            if (Math.abs(data[index]) < epsilon) {
                throw new SingularMatrixException();
                }
            inv.data[index] = 1.0 / data[index];
            }

        return inv;

        }

    public Matrix solve(Matrix b, double epsilon)
        throws SingularMatrixException {

        Matrix result = b.duplicate();

        for (int i = 0; i < columns; ++i) {
            double diag = data[i * (columns + 1)];
            if (Math.abs(diag) < epsilon) {
                throw new SingularMatrixException();
                }
            double inv = 1.0 / diag;

            NonNullRange range = result.getRangeForRow(i);
            for (int index = i * b.columns + range.begin;
                 index < i * b.columns + range.end;
                 ++index) {
                result.data[index] = inv * b.data[index];
                }
            }

        return result;

        }

    public NonNullRange getRangeForRow(int i) {
        return new NonNullRange(i, i + 1);
        }

    public NonNullRange getRangeForColumn(int j) {
        return new NonNullRange(j, j + 1);
        }

    }



/**
   COPYRIGHT AND LICENSE

   Copyright (c) 2001-2005, Luc Maisonobe
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   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   CONTRIBUTORS 'AS IS' AND ANY EXPRESS OR IMPLIED
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*/