線形方程式を解くための数値法列の主要素消去法

序文：教科書の解答の質を激しく非難しました!!!

import java.util.Scanner;

public class Gauss {
    static final int MAXN = 20;
    static double a[][] = new double[MAXN][MAXN];
    static double b[][] = new double[2][MAXN];//用来记录解出来的根,本题用一维数组即可,二维数组是为完全主元素消元法做准备
    static int num;

    public static void main(String[] args) {
        System.out.println("输入未知数个数:");
        Scanner sc = new Scanner(System.in);
        num = sc.nextInt();
        System.out.println("输入用矩阵表示的线性方程组:");
        for (int i = 0; i < num; i++) {//输入方程组
            for (int j = 0; j <= num; j++) {
                a[i][j] = sc.nextDouble();
            }
        }

        for (int i = 0; i < num; i++) {//初始化计数数列
            b[0][i] = i;
            b[1][i] = 0;
        }
        for (int j = 0; j < num - 1; j++) {
            paixu(j);

            dengjia(j);


        }

        for (int i = num - 1; i >= 0; i--) {
            jiefangcheng(i);
        }
        for (int j = 0; j < num; j++) {
            System.out.println("x" + (j + 1) + "=" + b[1][j]);
        }
    }

    static void dengjia(int jj) {//把原矩阵转化成三角形的
        for (int i = jj + 1; i < num; i++) {
            double k = a[i][jj] / a[jj][jj];
            for (int j = jj; j <= num; j++) {
                a[i][j] = a[i][j] - a[jj][j] * k;
            }
        }

    }

    static void jiefangcheng(int ii) {//解方程
        for (int j = ii + 1; j < num; j++) {
            a[ii][num] -= a[ii][j] * b[1][j];
        }
        b[1][ii] = a[ii][num] / a[ii][ii];

    }

    static void paixu(int jj) {//排序

        for (int j = jj; j < num-1; j++) {

            for (int k = jj; k < num - 1; k++) {

                if (Math.abs(a[k][jj]) < Math.abs(a[k + 1][jj])) {
                    for (int i = jj; i <= num; i++) {
                        double temp = a[k][i];
                        a[k][i] = a[k + 1][i];
                        a[k + 1][i] = temp;
                    }
                }


            }
        }
    }
}