1. Faculty of Applied Mathematics, Guangdong University of Technology, Guangzhou 510520, P. R. China
2. Department of Mathematics, Shantou University, Shantou 515063, P. R. China
3. Guangdong Provincial Key Lab of Digital Signals and Image Processing, Shantou University, Shantou, Guangdong, 515063, P. R. China
4. College of Mathematics, Jilin Normal University, Siping, Jilin 136000, P. R. China