1. Department of Computer Science and A.I., CITIC-UGR, University of Granada, 18071 Granada, Spain. E-mail: {jalcala,herrera}@decsai.ugr.es
2. Department of Electronics and Information, Politecnico di Milano, 20133 Milano, Italy. E-mail: nicolo.flugy@mail.polimi.it;bonarini@elet.polimi.it