1. Department of Applied Mathematics; National Sun Yat-sen University; Kaohsiung 80424 Taiwan
2. Department of Computer Science and Engineering; National Sun Yat-sen University; Kaohsiung 80424 Taiwan
3. Department of Mathematical Sciences; Fudan University; Shanghai 200433 China
4. Department of Applied Mathematics; I-Shou University; Kaohsiung 84001 Taiwan