1. Institute of Systems and Robotics, Department of Electrical Engineering and Computers, University of Coimbra, 3030-290 Coimbra, Portugal
2. Department of Electrical Engineering and Computers, University of Coimbra, 3030-290 Coimbra, Portugal
3. Computational Intelligence and Applications Research Group, Department of Computer Science, School of Science and Technology, Nottingham Trent University, Nottingham NG11 8NS, UK