package com.imsl.test.example.math;

import com.imsl.math.*;

/**
 * <p>
 * Solves a small linear system stored in sparse form. </p>
 *
 * A solution to a small linear system in which the coefficient matrix has been
 * stored in <a href="../../../math/SparseMatrix.html"><code>SparseMatrix</code></a> 
 * form is found. An initial guess of all ones is
 * set before solving the system.
 *
 * @see <a href="GenMinResEx3.java">Code</a>
 * @see <a href="doc-files/GenMinResEx3.out">Output</a>
 */
public class GenMinResEx3 implements GenMinRes.Function {

    static private SparseMatrix A;
    static private double a[] = {6.0, 10.0, 15.0, -3.0, 10.0,
        -1.0, -1.0, -3.0, -5.0, 1.0,
        10.0, -1.0, -2.0, -1.0, -2.0};
    static private double b[] = {10.0, 7.0, 45.0, 33.0, -34.0, 31.0};
    static private double xguess[] = {1.0, 1.0, 1.0, 1.0, 1.0, 1.0};
    static private int irow[] = {5, 1, 2, 1, 3, 3, 4,
        4, 4, 4, 0, 5, 5, 1, 3};
    static private int jcol[] = {5, 1, 2, 2, 3, 4, 0,
        5, 3, 4, 0, 0, 1, 3, 0};

    /**
     * Obtains the multiplication of the matrix <code>a</code> and the input
     * <code>p</code>. The result is returned in <code>z</code>.
     *
     * @param p a <code>double</code> array with
     * <code>p.length</code>=<code>a[0].length</code>
     * @param z a <code>double</code> array
     */
    @Override

    public void amultp(double p[], double z[]) {
        double[] result;
        result = A.multiply(A, p);
        System.arraycopy(result, 0, z, 0, z.length);
    }

    public static void main(String args[]) throws Exception {
        int n = 6;

        A = new SparseMatrix(n, n);
        for (int i = 0; i < a.length; i++) {
            A.set(irow[i], jcol[i], a[i]);
        }

        GenMinResEx3 atp = new GenMinResEx3();

        // Construct a GenMinRes object
        GenMinRes gnmnrs = new GenMinRes(n, atp);
        gnmnrs.setGuess(xguess);
        // Solve Ax = b
        new PrintMatrix("x").print(gnmnrs.solve(b));
    }
}