1. Department of Computer Science and Information Management, Providence University, 200, Sec. 7, Taiwan Blvd., Shalu District, Taichung City 43301, Taiwan
2. Department of Applied Mathematics, National Chung-Hsing University, 145 Xingda Rd., South District, Taichung City 402, Taiwan (Corresponding author), e-mail: tcyen@nchu.edu.tw
3. Department of Applied Mathematics, National Chung-Hsing University, 145 Xingda Rd., South District, Taichung City 402, Taiwan