NumericalMethod/GaussElimationMethod.cpp at master · AminKaiser/NumericalMethod · GitHub

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#include <bits/stdc++.h>
using namespace std;

double arr[100][100];
void print(int n)
{
        for(int i=0;i<n;i++)
        {
                for(int j=0;j<=n;j++)
                        cout<<arr[i][j]<<' ';
                cout<<endl;
        }
}

int main()
{
        freopen("in.txt","r",stdin);
        int n,i,j,k;
        cin>>n;


        for(i=0;i<n;i++)
        {
                for(j=0;j<=n;j++)
                {
                        cin>>arr[i][j];
                }
        }
//print(n); cout<<endl;

/// use for Pivoting
        for(i=0;i<n-1;i++)
        {
                double tmp=0; int best_row;
                for(j=i;j<n;j++)
                {
                        if(tmp<fabs(arr[j][i]))
                        {
                                tmp=fabs(arr[j][i]);
                                best_row=j;
                        }
                }
                if(best_row!=i)for(j=i;j<=n;j++)
                {
                        swap(arr[i][j],arr[best_row][j]);
                }
print(n); cout<<endl;

/// end Pivoting

                if(fabs(arr[i][i])<.000001) return cout<<"no solution",0;

                tmp=arr[i][i];
                for(j=i;j<=n;j++)
                {
                        arr[i][j]=arr[i][j]/tmp;
                }

                double tmp2;
                for(j=i+1;j<n;j++)
                {
                        tmp2=arr[j][i];
                        for(k=i;k<=n;k++)
                        {
                                tmp=arr[i][k]*tmp2;
                                arr[j][k]=arr[j][k]-tmp;
                        }
                }
        }

        for(i=n-1;i>=0;i--)
        {
                double tmp=0;
                for(j=i+1;j<n;j++)
                {
                        tmp+=(arr[i][j]*arr[j][n]);
                }
                tmp=arr[i][n]-tmp;
                arr[i][n]=tmp/arr[i][i];
        }

        for(i=0;i<n;i++)
        {
                cout<<'X'<<i<<'='<<arr[i][n]<<endl;
        }


	return 0;
}