math - Guass

#include<bits/stdc++.h>
#define EPS    1e-9
using namespace std;
struct Gauss{
    /*          1  1 |  3  5
                1 -1 |  1  6
                {x+y=3}{x+y=5}
                {x-y=1}{x-y=6}
    */
    void show(vector<vector<double> > a, vector <vector< double> > b)
    {
        for(int i= 0;i< a.size();i ++) {
            for(int j= 0;j < a[i].size(); j ++) printf("%5.2lf ",a[i][j]);
            printf("| ");
            for(int j = 0; j < b[i].size(); j ++) printf("%5.2lf ",b[i][j]);
            printf("\n");
        }
    }
    int gauss(vector< vector< double > > &a , vector< vector<double > > &b)
    {
        // AX = B;
        // Here n -> # of equations, m = number of column in A, p = # column in B
        // The function returns the rank of the matrix
        int n = a.size(), m= a[0].size() , p = b[0].size();
        int r = 0;

        for(int c = 0; c < m  && r < n ; c ++ ) {
            int j = r;
            for(int i = r+1; i < n; i ++ ) {
                if(fabs(a[i][c]) > fabs(a[j][c])) j= i;
            }
            if(fabs(a[j][c]) < EPS) continue;
            if(j!=r)swap(a[j],a[r]), swap(b[j],b[r]);
            double s = 1./a[r][c];

            for(int i = 0; i < m ; i ++ ) a[r][i] *= s;
            for(int i = 0; i < p ; i ++ ) b[r][i] *= s;
            for(int i=0;i < n ;i ++) if(i!=r) {
                double t = a[i][c];
                for(int j = 0; j < m ; j ++ ) a[i][j] -= t * a[r][j];
                for(int j = 0; j < p ; j ++ ) b[i][j] -= t * b[r][j];
            }
            r++;
        }
        return r;
    }
}g;

int main()
{
    double a[][2] = {{1,1},{1,-1}};
    double b[][2] = {{3,1},  {5,6}};

    vector< vector<double> > A(2, vector<double> (2,0));
    for(int i = 0;i<2; i ++) {
        for(int j = 0; j < 2;j++) {
            A[i][j] = a[i][j];
        }
    }

    vector< vector<double> > B(2 , vector<double> (2,0));
    for(int i = 0; i <2;i ++ ) {
        for(int j = 0; j < 2; j ++ ) B[j][i] = b[i][j];
    }


    g.gauss(A,B);
    for(int i = 0; i < 2;i ++) printf("%lf ",B[i][0]); puts("");
    for(int i = 0; i < 2;i ++) printf("%lf ",B[i][1]);
    return 0;
}