gaussi

#include <iostream>
#include <cstdio>
#include <math.h>
#include <time.h>
#include <stdlib.h>
using namespace std;
const int MAXN = 10000;
double a[MAXN][MAXN];
double b[MAXN];
double x[MAXN];
int main()
{
    int n=3;
    double l;
    int i,number;
    double sum;
    srand((unsigned) time(NULL)); 
    printf("a[][]:
");
    for(int i = 0;i<n;i++){
        for(int j = 0;j<n;j++){
            number = rand() % 11;
            a[i][j]=(double)(number*1.131121);
            printf("%f  ",a[i][j]);
            sum+=a[i][j];
        }
        cout << endl;
        b[i]=sum;
        sum=0;
    }
    ///消元过程
    for(int k = 0;k<n-1;k++){///消元行
        for(int i = k+1;i<n;i++){///被消元行
            l = a[i][k]/a[k][k];
            for(int j = k;j<n;j++){
                a[i][j]-=l*a[k][j];
            }
            b[i]-=b[k]*l;
        }
    }
    ///回带过程
    for(int i = n-1;i>=0;i--){
            x[i] = b[i];
        for(int j = n-1;j>i;j--){
            x[i] -= a[i][j]*x[j];
        }
        x[i] /= a[i][i];
    }
    ///高斯消元法输出 
    printf("x[]:(gaussi)
");
     for(int i = 0;i<n;i++){
        printf("%.6f  ",x[i]);
    }
    cout << endl;

    //------------------------- 

    double maxs;
    ///消元过程
    for(int k = 0;k<n-1;k++){///消元行
        int cur = k;
        maxs = fabs(a[k][k]);
        for(int i = k;i<n;i++)if(maxs<fabs(a[i][k])){maxs = fabs(a[i][k]);cur = i;}///选主元
        if(cur != k){
            double temp;
            for(int j = k;j<n;j++){
                temp = a[k][j];
                a[k][j] = a[cur][j];
                a[cur][j] = temp;
            }
            temp = b[k];b[k] = b[cur];b[cur] = temp;
        }

        for(int i = k+1;i<n;i++){///被消元行
            l = a[i][k]/a[k][k];
            for(int j = k;j<n;j++){
                a[i][j]-=l*a[k][j];
            }
            b[i]-=b[k]*l;
        }
    }

    ///回带过程
    for(int i = n-1;i>=0;i--){
            x[i] = b[i];
        for(int j = n-1;j>i;j--){
            x[i] -= a[i][j]*x[j];
        }
        x[i] /= a[i][i];
    }
    ///高斯列主元素消元法输出 
     printf("x[]:(gaussi_row)
");
     for(int i = 0;i<n;i++){
        printf("%.6f  ",x[i]);
    }
    cout << endl;
    return 0;
}