Gaussian_elimination.c

#include<stdio.h>

//項の数
#define N 2

signed main(){
    double a[N][N+1];
    double d;
    int i, j, k;

    for(i = 0; i < N; i++){
        for(j = 0; j < N+1; j++){
            scanf("%lf", &a[i][j]);
        }
    }

    //前進消去
    for(k = 0; k < N - 1; k++){
        for(i = k+1; i < N; i++){
            d = a[i][k] / a[k][k];
            for(j = k + 1; j <= N; j++){
                a[i][j] = a[i][j] - a[k][j] * d;
            }
        }
    }
    
    //後退代入
    for(i = N -1; i >= 0; i--){
        d = a[i][N];
        for(j = i + 1; j < N; j++){
            d = d - a[i][j] * a[j][N];
        }
        a[i][N] = d / a[i][i];
    }
    
    for(k = 0; k < N; k++){
        printf("%f\n", a[k][N]);
    }
    return 0;
}