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MTH6142 / MTH6142P Complex networks
发布时间:2022-05-16
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Main Examination period 2017
MTH6142 / MTH6142P
Complex networks
Question 1. [30 marks]
Structural properties of a given network.
Consider the adjacency matrix A of a network of size N – ; given by
╱ 、
A – ... .
a) Is the network directed or undirected? (←_;╱;Jy y)_≠)礻;wμ≠)
b) Draw the network.
c) How many weakly connected components are there in the network? Which are the nodes in each weakly connected component?
[2]
[4]
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d) How many strongly connected components are there in the network? Which
are the nodes in each strongly connected component?
e) Is there an out-component in the network? If yes, indicate the nodes in the out-component of the network.
f) Determine the in-degree sequence {k1(i)n , k2(in), k3(in), k4(in)} and the out-degree sequence {k1(o)ut , k2(out), k3(out), k4(out)}.
g) Determine the in-degree distribution Pin (k) and the out-degree distribution Pout (k).
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[4]
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h) Calculate the eigenvector centrality xi of each node i – 1, 2, . . . , N of the network with adjacency matrix A given by Eq. (1).
To this end start from the initial guess x(0) – 1 where 1 is the N-dimensional column vector of elements 1i – 1 Vi – 1, 2 . . . , N.
Consider the iteration
x(n) – Ax(n一1)
for n e N.
Finally evaluate the eigenvector centrality xi of each node i of the network by calculating the limit
xi – n(i) N (n) .
i) Is the result obtained in point h) expected? (6左y←)
[8]
[2]
Question 2. [35 marks] Diameter and clustering coefficient of networks a) Which is the undirected network of N nodes with smallest diameter? Does this network have the small-world distance property? 6左y← b) Which is the undirected network of N nodes which is connected and has the largest diameter? Does this network have the small-world distance property? 6左y← c) Consider a random Poisson network with average degree (k) – ; and total number of nodes N. Indicate with l the average shortest path in the network.
i) Using the properties of the generating function evaluate the average branching ratio of a node reached by following a link given by (b) –
ii) Approximate the number of nodes Nd at distance d > 1 from a random node of the network as Nd – (k) ╱ iii) Using the properties of the geometric sum, evaluate the total number Nd≤e of nodes at distance 0 2 d 2 l from a random node of the network. iv) Impose that all the nodes of the Poisson network can be found within a distance d 2 l from any random node. Using the result obtained in (ii), express the average distance l of the Poisson network in terms of the total number of nodes N.
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