1. Department of Economics, Division of Mathematics, Informatics and Quantitative Methods, National and Kapodistrian University of Athens (NKUA), 1, Sofokleous str, 4th floor, P.O. 10559, Greece
2. Systems and Control Engineering Centre, Department of Engineering, School of Mathematics, Computer Science and Engineering, City University of London, Northampton Square, London EC1V 0HB, UK