#include <stdio.h>
#include <math.h>

#define N 3
double A[N][N]= {{1,2,3},{4,5,7},{-3,2,8}};
double *P[N];

void matprint(double B[N][N]){
    for(int i=0;i<N;i++){
        for(int j=0;j<N;j++){
            printf("%g ",B[i][j]);
        }
        printf("\n");
    }
}
void matmemprint(double B[N][N]){
    for(int i=0;i<N;i++){
        for(int j=0;j<N;j++){
            printf("%p:%g ",&B[i][j],B[i][j]);
        }
        printf("\n");
    }
}
void pointermatprint(double *P[N]){
    for(int i=0;i<N;i++){
        for(int j=0;j<N;j++){
            printf("%g ",P[i][j]);
        }
        printf("\n");
    }
}
int main(){
    matprint(A);
    matmemprint(A);
    for(int i=0;i<N;i++) P[i]=&A[i][0];
    pointermatprint(P);
    double *t=P[0]; P[0]=P[1]; P[1]=t;
    printf("after swapping\n");
    pointermatprint(P);
    for(int i=1;i<N;i++){
        double alpha=P[i][0]/P[0][0];
        for(int j=0;j<N;j++){
            P[i][j]-=alpha*P[0][j];
        }
        P[i][0]=alpha;
    }
    printf("after some elimination\n");
    pointermatprint(P);
    t=P[1]; P[1]=P[2]; P[2]=t;
    printf("after swaping r2 with r3\n");
    pointermatprint(P);
    for(int i=2;i<N;i++){
        double alpha=P[i][1]/P[1][1];
        for(int j=1;j<N;j++){
            P[i][j]-=alpha*P[1][j];
        }
        P[i][1]=alpha;
    }
    printf("after the last elimination\n");
    pointermatprint(P);
//    printf("the original matrix\n");
//    matprint(A);
    return 0;
}