1. Department of Mathematics, Zhejiang University, Hangzhou 310027, China
2. Department of Applied Mathematics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
3. College of Mathematics and Information Science, Hebei Normal University and Hebei Key Laboratory of Computational Mathematics and Applications, Shijiazhuang 050024, China
4. Department of Information Management, Yuan Ze University, Chungli 32003, Taiwan