1. Department of Mathematics and Statistics, Oakland University, Rochester, Michigan 48309, USA
2. Department of Computer Science, Fuzhou University, Fuzhou, Fujian 350116, PR China
3. School of Mathematics and Statistics, Qinghai Normal University, Xining, Qunghai 810008, PR China
4. School of Mathematical Science & Institute of Mathematics, and Key Laboratory of Ministry of Education Numerical Simulation of Large Scale Complex Systems, Nanjing Normal University, Nanjing, Jiangsu 210023, PR China