数值方法完全主元素消元法解线性方程组

原题排序成这样就行了

本程序是排成这样,懒得改了,差不多就行,嘿嘿

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];//我想多了,这里用一维数组就好
    static int num;
    static int x_max;
    static int y_max;

    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; j++) {
            a[num][j] = j;
        }
        for (int j = 0; j < num - 1; j++) {
            findMax(j);
        
           sort1(j);

            findMax(j);
       
            sort2(j);

            dengjia(j);


        }

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

    static void sort1(int jj) {//行排序
        for (int j = jj; j < num - 1; j++) {

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

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


            }
        }
    }

    static void sort2(int jj) {//列排序
        for (int j = jj; j < num - 1; j++) {

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

                if (Math.abs(a[y_max][k]) < Math.abs(a[y_max][k+1])) {
                    for (int i = 0; i <= num; i++) {
                        double temp = a[i][k];
                        a[i][k] = a[i][k + 1];
                        a[i][k + 1] = temp;
                    }
                }


            }
        }
    }

    static void findMax(int jj) {
        double max = 0;
        for (int i = jj; i < num; i++) {
            for (int j = jj; j < num; j++) {
                if (Math.abs(a[i][j]) > Math.abs(max)) {
                    max = a[i][j];
                    y_max = i;
                    x_max = 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];

    }

}