1. Guangxi Key Laboratory of Universities Optimization Control and Engineering Calculation, and College of Sciences, Guangxi University for Nationalities, Nanning530006, Guangxi Province, P. R. China
2. Institute of Computer Science, Faculty of Mathematics and Computer Science, Jagiellonian University, ul. Lojasiewicza 6, 30-348Krakow, Poland
3. Département de Mathématiques, Université de Perpignan, 66860Perpignan, France