A network may experience random failure in its components. Resiliency against failures is vital for the proper functioning of the network. The degree–degree correlation plays a key role in determining the resiliency of the networks and can be measured by calculating assortativity [7,32,53]. (9)r=E−1∑ijiki−[E−1∑i12(ji+ki)]2E−1∑i12(ji2+ki2)−[E−1∑i12(ji+ki)]2 where ji and ki are the degrees of the nodes, and E represents the total number of edges. For r = 0, there is no correlation; r < 0 means that the network is disassortative; and r > 0 shows that the network is assortative.
