Consider a directed random graph of the kind discussed in Section 13.11.
a) If the in- and out-degrees of vertices are uncorre1ated, i.e., if the joint in/outdegree distribution Pjk is a product of separate functions of j and k, show that a giant strongly connected component exists in the graph if and only if c(c -1) > a, where c is the mean degree, either in or out.
b) In real directed graphs the degrees are usually correlated (or anti-correlated). The correlation can be quantified by the covariance ρ of in- and out-degrees. Show that in the presence of correlations, the condition above for the existence of a giant strongly connected component generalizes to c(c - 1) + ρ >O.
c) In the World Wide Web the in- and out-degrees of the vertices have a measured covariance of about ρ = 180. The mean degree is around c = 4.6. On the basis of these numbers, do we expect the Web to have a giant strongly connected component?