Gauss seidel

void solver(int n, int itr, double tol, double[] a, double[] b, double[] x)
  {
    double[] r = new double[n];
    double[] x_old = new double[n];
    double[] x_new = new double[n];

    for (int j = 0; j < itr; j++)
    {
      for (int i = 0; i < n; i++)
      {
        x_old[i] = x[i];
      }

      for (int i = 0; i < n; i++)
      {
        x_new[i] = (b[i] - dot(a, x_old, i)) / a[i, i];
      }

      for (int i = 0; i < n; i++)
      {
        x[i] = x_new[i];
      }

      for (int i = 0; i < n; i++)
      {
        r[i] = b[i] - dot(a, x, i);
      }