Matrix multiplication using Gaussian elimination.

GaussianElimination.java

/*
* Date created, Sunday 26th March, 2009.
* Coded by: Celestine Ezeokoye
*/

package gaussianelimination;

import java.util.Scanner;

public class GaussianElimination {

    public static void main(String[] args) {
        double[][] values = null;
        double[] rhs = null;
        acceptInput(values, rhs);

    }

    private static void acceptInput(double[][] values, double[] answerPart) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter the size of the array: ");
        int size = input.nextInt();
        values = new double[size][size];
        answerPart = new double[size];
        for (int i = 0; i < values.length; i++) {
            for (int j = 0; j < values[i].length; j++) {
                System.out.print("Enter the value for index (" + (i + 1) + "," + (j + 1) + "): ");
                values[i][j] = input.nextDouble();
            }
            System.out.print("Enter value for the augmented part at row (" + (i + 1) + "): ");
            answerPart[i] = input.nextDouble();
        }
        reduceRows(values, answerPart);
    }

    private static double[] backSubstitute(double[][] values, double[] answerPart) {
        double[] answers = new double[answerPart.length];
        for (int i = values.length - 1; i >= 0; i--) {
            double temp = 0;
            for (int j = values[i].length - 1; j >= i; j--) {
                if (j == i) {
                    temp = (answerPart[i] - temp) / values[i][j];
                } else {
                    temp += values[i][j] * answers[j];
                }
            }
            answers[i] = temp;
        }

        System.out.println("The answers are: \n");
        for (int i = 0; i < answers.length; i++) {
            System.out.printf("X%d is %.2f\n", (i + 1), answers[i]);
        }
        System.out.println();
        return answers;
    }

    private static double[] reduceRows(double[][] values, double[] answerPart) {
        System.out.println("Reducing rows...\n");
        double pivot = 0.0, pivotRatio = 0.0;
        for (int i = 1; i < values.length; i++) {
            for (int j = i; j < values.length; j++) {
                pivot = values[j][i - 1];
                pivotRatio = pivot / values[i - 1][i - 1];
                for (int k = i - 1; k < values[j].length; k++) {
                    values[j][k] = (pivotRatio * values[i - 1][k]) - values[j][k];
                }
                answerPart[j] = (pivotRatio * answerPart[i - 1]) - answerPart[j];
            }

        }
        System.out.println("The Augmented reduced rows are:\n");
        for (int i = 0; i < values.length; i++) {
            for (int j = 0; j < values[i].length; j++) {
                if (j != values[i].length - 1) {
                    System.out.printf("%.2f,\t", values[i][j]);
                } else {
                    System.out.printf("%.2f|\t", values[i][j]);
                }
            }
            System.out.printf("%.2f\n", answerPart[i]);
        }
        System.out.println();
        return backSubstitute(values, answerPart);
    }
}