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""" Example of parallel implementation of betweenness centrality using the multiprocessing module from Python Standard Library. The function betweenness centrality accepts a bunch of nodes and computes the contribution of those nodes to the betweenness centrality of the whole network. Here we divide the network in chunks of nodes and we compute their contribution to the betweenness centrality of the whole network. """ from multiprocessing import Pool import time import itertools import networkx as nx def chunks(l, n): """Divide a list of nodes `l` in `n` chunks""" l_c = iter(l) while 1: x = tuple(itertools.islice(l_c, n)) if not x: return yield x def _betmap(G_normalized_weight_sources_tuple): """Pool for multiprocess only accepts functions with one argument. This function uses a tuple as its only argument. We use a named tuple for python 3 compatibility, and then unpack it when we send it to `betweenness_centrality_source` """ return nx.betweenness_centrality_source(*G_normalized_weight_sources_tuple) def betweenness_centrality_parallel(G, processes=None): """Parallel betweenness centrality function""" p = Pool(processes=processes) node_divisor = len(p._pool)*4 node_chunks = list(chunks(G.nodes(), int(G.order()/node_divisor))) num_chunks = len(node_chunks) bt_sc = p.map(_betmap, zip([G]*num_chunks, [True]*num_chunks, [None]*num_chunks, node_chunks)) # Reduce the partial solutions bt_c = bt_sc for bt in bt_sc[1:]: for n in bt: bt_c[n] += bt[n] return bt_c if __name__ == "__main__": G_ba = nx.barabasi_albert_graph(1000, 3) G_er = nx.gnp_random_graph(1000, 0.01) G_ws = nx.connected_watts_strogatz_graph(1000, 4, 0.1) for G in [G_ba, G_er, G_ws]: print("") print("Computing betweenness centrality for:") print(nx.info(G)) print("\tParallel version") start = time.time() bt = betweenness_centrality_parallel(G) print("\t\tTime: %.4F" % (time.time()-start)) print("\t\tBetweenness centrality for node 0: %.5f" % (bt)) print("\tNon-Parallel version") start = time.time() bt = nx.betweenness_centrality(G) print("\t\tTime: %.4F seconds" % (time.time()-start)) print("\t\tBetweenness centrality for node 0: %.5f" % (bt)) print("")