def estimate_time(self):
        pn_temp = OpenPNM.Network.TestNet()
        graph = pn_temp.create_adjacency_matrix(sprsfmt='csr')
        self._net.tic()
        path = spgr.shortest_path(csgraph=graph, method='D', directed=False)
        t = self._net.toc(quiet=True)
        N = 125
        k = 6
        O = t / (N * (N * k + N * sp.log(N)))
        N = self._net.num_pores()
        k = sp.median(self._net.num_neighbors(pores=self._net.pores()))
        t_est = O * (N * (N * k - N * sp.log(N)))
        logger.info('Based on the network size and PC performance, ' +
                    'this algorithm will require: ', t_est, ' seconds')
        return
dataset/ETHPy150Open PMEAL/OpenPNM/OpenPNM/Algorithms/__Tortuosity__.py/Tortuosity.estimate_time/operator `+` -> `-`