Gaus

data.txt

0.02 0.01 0 0 0.02
1 2 1 0 1
0 1 2 1 4
0 0 100 200 800

main.cpp

// aproksymacja.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
// #include <mkl_lapack.h> 
#include <fstream>
#include <string>
#include <sstream>
#include <math.h>

using namespace std; 

const int MAX_SIZE = 1000;

int equations_count = 0, col_count = 0;
double equations[MAX_SIZE][MAX_SIZE] = { 0 };
double x[MAX_SIZE] = { 0 };

void print_equations(){
  for(int i=0;i<equations_count; i++){
    for(int j=0;j<col_count; j++){
      cout << equations[i][j]<< "\t";
    }
    cout << endl;
  }
  cout<< endl;
}

int find_index_of_max_in_col(int col, int first_row){
  int max_val = abs(equations[first_row][col]);
  int index_of_max = first_row;
  for(int i = first_row+1; i<equations_count; i++){
    if(abs(equations[i][col]) > max_val){
      max_val = abs(equations[i][col]);
      index_of_max = i;
    }
  }
  return index_of_max;
}

void swap_rows(int row_a, int row_b){
  double tmp = 0;
  for(int j=0;j<col_count;j++){
    tmp = equations[row_a][j];
    equations[row_a][j] = equations[row_b][j];
    equations[row_b][j] = tmp;
  }
}

void pivot(int row, int col){
  int index_of_max = find_index_of_max_in_col(col, row);
  if(index_of_max != row){
    swap_rows(index_of_max, row);
  }
}

bool is_zero(int row, int col){
  return equations[row][col] == 0;
}

void eliminate(int row, int col){
  for(int i = row+1; i < equations_count; i++){
    double curr_multiplier = equations[i][col] / equations[row][col];
    for(int j = col; j<col_count; j++){
      equations[i][j] -= curr_multiplier * equations[row][j];
    }
  }
}

void purge(){
  for(int i=0;i<equations_count;i++){
    print_equations();
    pivot(i,i);
    if(is_zero(i,i)) {
      return;
    }
    eliminate(i,i);
    print_equations();
  }
}

double calc_x(){
  x[equations_count] = 1;
  for(int i=equations_count-1; i>=0; i--){
    double b_i = 1.0 * equations[i][col_count-1];
    cout << "bi" << b_i<<endl;
    double counter = b_i;
    for(int j=col_count-2; j>i; j--){
      counter -= x[j+1]*equations[i][j];
      cout << "c" << counter<<endl;

    }
    // counter -= equations[i][i];
    x[i] = counter / equations[i][i];
    cout << x[i] <<endl;
    cout << endl<< endl;
  }
}

int main()
{
	string line;
	ifstream file("data.txt");
	double suma = 0;

	if (file.is_open())
	{
    double elem;
		while (getline(file, line))
		{
			istringstream ss(line);

      int j = 0;
      while(ss >> elem){
        equations[equations_count][j++] = elem;
      }

      col_count = max(col_count, j);
			equations_count++;
		}
	}

  purge();

  calc_x();

  for(int i=0;i<equations_count; i++){
    cout << "x_" << i << "=" << x[i] << endl;
  }

  return 0;

	// // approx(3);



	// // Results

	// cout << "Liczba wezlow: " << args_count << endl
	// 	<< endl;

	// for (int i = 0; i < args_count; i++)
	// {
	// 	cout << "x" << i << "=" << xtab[i] << "\t";
	// 	cout << "f(" << xtab[i] << ")=" << ytab[i] << endl;
	// }


	// return 0;
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file
/*
1	1
3	2
4	4
6	4
8	5
9	7
11	8
14	9
*/