Hi Tiago, thanks for your swift reply. Here is a variant of the Price network from the Quick Start Section of your documentation where I added random integers as edge weights. When I run the gt.minimize_blockmodel_dl command I get the same crash as with my own network. #! /usr/bin/env python from numpy.random import * seed(42) import graph_tool.all as gt g = gt.Graph() v_age = g.new_vertex_property("int") e_age = g.new_edge_property("int") e_weight = g.new_edge_property("int") N = 100000 v = g.add_vertex() v_age[v] = 0 vlist = [v] for i in range(1, N): v = g.add_vertex() v_age[v] = i i = randint(0, len(vlist)) target = vlist[i] # add edge and random edge weight e = g.add_edge(v, target) e_age[e] = i e_weight[e] = randint(1,6) vlist.append(target) vlist.append(v) g.vertex_properties["age"] = v_age g.edge_properties["age"] = e_age g.edge_properties["weight"] = e_weight state = gt.minimize_blockmodel_dl(g) print(state.B) state_w = gt.minimize_blockmodel_dl(g, eweight=g.edge_properties["weight"], multigraph = True) print(state_w.B) I don't know if it helps, but here is an additional message that pops up in the Terminal directly before the breakdown: Python(2069,0x7fff725f8300) malloc: *** error for object 0x7fb36c9fc068: incorrect checksum for freed object - object was probably modified after being freed. *** set a breakpoint in malloc_error_break to debug Please let me know if you need any other information. Thanks a lot, Jan -- 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.