Dear Tiago, When I use this, there is a error: Traceback (most recent call last): File "/home/workspace/work1/renren.py", line 127, in <module> find_sub_g() File "/home/workspace/work1/renren.py", line 97, in find_sub_g new_g.purge_vertices() File "/usr/lib/python2.7/dist-packages/graph_tool/__init__.py", line 1850, in purge_vertices new_g = Graph(self, prune=(True, False, False)) File "/usr/lib/python2.7/dist-packages/graph_tool/__init__.py", line 1121, in __init__ vorder.fa = numpy.arange(gv.num_vertices()) File "/usr/lib/python2.7/dist-packages/graph_tool/__init__.py", line 567, in <lambda> lambda self, v: self.__get_set_f_array(v, False), File "/usr/lib/python2.7/dist-packages/graph_tool/__init__.py", line 562, in __get_set_f_array a[m] = v TypeError: array cannot be safely cast to required type What are the reasons ? Thank you for your help. Best. vcongz -- 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.