docs: protected double computeQij(double[][] qij, double[][] solution) {
      double qij_sum = 0;
      for(int i = 1; i < qij.length; i++) {
        final double[] qij_i = qij[i], vi = solution[i];
        for(int j = 0; j < i; j++) {
          qij_sum += qij_i[j] = qij[j][i] = MathUtil.exp(-sqDist(vi, solution[j]));
        }
      }
      return qij_sum * 2; // Symmetry
    }