Why isn't it converging?

[scar95]

Guys I got this code, which uses the jacobi method to find the solution of a system of equations. The problem is, it's not converging, why?

#include <iostream>  //libraries
#include <cmath>
using namespace std;
const int EPSILON = 1e-8; //global const to be used for approximations
int main ()
{
    const int SIZE = 4;                //size of the arrrays
    double x[SIZE] = {};               //1D x array
    double A[SIZE][SIZE] = {           //2D A array
        {9, -4, -2, 0},
        {-4, 17, -6, -3},
        {-2, -6, 14, -6},
        {0, -3, -6, 11}
    };

    double b[SIZE] = {24, -16, 0, 18};
    double newx[4];
    bool converge = false; //setting the initial convergence to false
    cout << "Please enter an initial guess to the solution" << endl;
    cin >> x[0] >> x[1] >> x[2] >> x[3];                //the guess

    while ( converge == false )
    {
        newx[0] =(1/A[0][0])*(b[0] - ((A[0][1]*x[1]) + (A[0][2]*x[2]) + (A[0][3]*x[3])));
        newx[1] =(1/A[1][1])*(b[1] - ((A[1][0]*x[0]) + (A[1][2]*x[2]) + (A[1][3]*x[3])));
        newx[2] =(1/A[2][2])*(b[2] - ((A[2][0]*x[0]) + (A[2][1]*x[1]) + (A[2][3]*x[3])));
        newx[3] =(1/A[3][3])*(b[3] - ((A[3][0]*x[0]) + (A[3][1]*x[1]) + (A[3][2]*x[2])));

        converge = abs(newx[0] - x[0]) < EPSILON   //checking convergence
            && abs(newx[1] - x[1]) < EPSILON
            && abs(newx[2] - x[2]) < EPSILON
            && abs(newx[3] - x[3]) < EPSILON;

        x[0] = newx[0];
        x[1] = newx[1];
        x[2] = newx[2];
        x[3] = newx[3];

        cout << x[0] << "," << x[1] << "," << x[2] << "," << x[3] << endl;
    }
}

When I try entering 1,1,1,1 for example the loop never ends...

[OxBADC0DE]

Even in the while loop, nothing alters the bool value of converge which has already been initialized as false. Its an endless loop because converge stays false.

[scar95]

so how do i fix it?

[MiiNiPaa]

because you never bother to change converge to true inside loop.

[scar95]

yes I got that, but what should I do?
Start an if statement that includes all the abs()< EPSILON, and set converge to true?

[scar95]

if (abs(newx[0] - x[0]) < EPSILON   //checking convergence
            && abs(newx[1] - x[1]) < EPSILON
            && abs(newx[2] - x[2]) < EPSILON
            && abs(newx[3] - x[3]) < EPSILON)
        {
            converge = true;
        }

still not converging

[ne555]

const int EPSILON = 1e-8; //0

[scar95]

what do you mean?

[OxBADC0DE]

What he means is this:

const int EPSILON = 1e-8;

will produce 0 because it is of type int.