  We investigate the degree-degree correlations in the Erdos-Renyi networks,
the growing exponential networks and the scale-free networks. We demonstrate
that these correlations are the largest for the exponential networks. We
calculate also these correlations in the line graphs, formed from the
considered networks. Theoretical and numerical results indicate that all the
line graphs are assortative, i.e. the degree-degree correlation is positive.

Disordered Systems and Neural Networks;Physics and Society