1. Department of Mathematics, Shanghai University, Shanghai, P.R. China
2. Key Laboratory of Numerical Simulation of Sichuan Province, Neijiang Normal University, Neijiang, Sichuan, P.R. China
3. School of Mathematical Sciences, University of Electronic Science and Technology of China, Chengdu, Sichuan, P.R. China
4. School of Economic Mathematics, Southwestern University of Finance and Economics, Chengdu, Sichuan, P.R. China