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