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Introduction to the Modeling and Analysis of Complex Systems

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16.3. SIMULATING DYNAMICS OF NETWORKS 359Exercise 16.15 Simulate <strong>the</strong> Barabási-Albert network growth model with m = 1,m = 3, <strong>and</strong> m = 5, <strong>and</strong> see how <strong>the</strong> growth process may be affected by <strong>the</strong>variation <strong>of</strong> this parameter.Exercise 16.16 Modify <strong>the</strong> preferential node selection function so that <strong>the</strong> nodeselection probability p(i) is each <strong>of</strong> <strong>the</strong> following:• independent <strong>of</strong> <strong>the</strong> node degree (r<strong>and</strong>om attachment)• proportional <strong>to</strong> <strong>the</strong> square <strong>of</strong> <strong>the</strong> node degree (strong preferential attachment)• inversely proportional <strong>to</strong> <strong>the</strong> node degree (negative preferential attachment)Conduct simulations for <strong>the</strong>se cases <strong>and</strong> compare <strong>the</strong> resulting network <strong>to</strong>pologies.Note that NetworkX has a built-in graph genera<strong>to</strong>r function for <strong>the</strong> Barabási-Albertscale-free networks <strong>to</strong>o, called barabasi_albert_graph(n, m). Here, n is <strong>the</strong> number <strong>of</strong>nodes, <strong>and</strong> m <strong>the</strong> number <strong>of</strong> edges by which each newcomer node is connected <strong>to</strong> <strong>the</strong>network.Here are some more exercises <strong>of</strong> dynamics <strong>of</strong> networks models, for your fur<strong>the</strong>r exploration:Exercise 16.17 Closing triangles This example is a somewhat reversed version<strong>of</strong> <strong>the</strong> Watts-Strogatz small-world network model. Instead <strong>of</strong> making a local,clustered network <strong>to</strong> a global, unclustered network, we can consider a dynamicalprocess that makes an unclustered network more clustered over time. Here are<strong>the</strong> rules:• The network is initially r<strong>and</strong>om, e.g., an Erdős-Rényi r<strong>and</strong>om graph.• In each iteration, a two-edge path (A-B-C) is r<strong>and</strong>omly selected from <strong>the</strong> network.• If <strong>the</strong>re is no edge between A <strong>and</strong> C, one <strong>of</strong> <strong>the</strong>m loses one <strong>of</strong> its edges (butnot <strong>the</strong> one that connects <strong>to</strong> B), <strong>and</strong> A <strong>and</strong> C are connected <strong>to</strong> each o<strong>the</strong>rinstead.This is an edge rewiring process that closes a triangle among A, B, <strong>and</strong> C, promotingwhat is called a triadic closure in sociology. Implement this edge rewiringmodel, conduct simulations, <strong>and</strong> see what kind <strong>of</strong> network <strong>to</strong>pology results from

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