Bicyclic digraphs with maximal energy

If D is a digraph with n vertices then the energy of D is defined as epsilon(D) = Sigma(n)(k=1) vertical bar Re(z(k))vertical bar, where Re (z(1)), ..., Re(z(n)) are the real parts of the eigenvalues z(1), ..., z(n) of D. In this paper we solve a problem proposed in Khan et al. (2015), we find the maximal value of the energy over the set of all bicyclic digraphs B-n with n vertices. (C) 2016 Elsevier Inc. All rights reserved.