Hi Tiago, Thanks for the reply. I still have the same issue. I am running the following code in Jupyter prop = g.new_vertex_property("vector<double>") for i in xrange(n): prop[i] = [1 + i,1 + i] #openmp_set_num_threads(1) pos = sfdp_layout(g, gamma=10.0, mu=10.0, mu_p=10.0, verbose = False, pos=prop) I disabled the openmp command because it gives me an error that it's not enabled anyway: "OpenMP was not enabled during compilation". Every time that I press shift + enter in Jupyter to re-run the above piece of code (without running anything else in-between) I get a different pos output. Kimon -- View this message in context: http://main-discussion-list-for-the-graph-tool-project.982480.n3.nabble.com/... Sent from the Main discussion list for the graph-tool project mailing list archive at Nabble.com.