1. School of Computer and Software Engineering, Xihua University, Chengdu, Sichuan 610039, P. R. China
2. School of Electrical Engineering and Electronic Information, Xihua University, Chengdu, Sichuan 610039, P. R. China
3. Research Group of Natural Computing, Department of Computer Sciences and Artificial Intelligence, School of Computer Engineering, University of Seville, 41012, C. P. Sevilla, Spain