code: def _sort_tau_by_y(self, y):
          tau_y = self.tau_matrix[:, y]
          tau_y[y] = np.NaN
          temp = np.empty([self.n_nodes, 3])
          temp[:, 0] = np.arange(self.n_nodes)
          temp[:, 1] = tau_y
          temp[:, 2] = abs(tau_y)
          temp[np.isnan(temp)] = -10
          tau_sorted = temp[temp[:, 2].argsort()[::-1]]
          return tau_sorted