1. Department of Applied Mathematics, National University of Kaohsiung, Kaohsiung 811, Taiwan, ROC, m0974103@mail.nuk.edu.tw; speu@nuk.edu.tw
2. Mathematics Faculty, National Pingtung Institute of Commerce, Pingtung 900, Taiwan, ROC, tsfu@npic.edu.tw
3. Department of Computer Science and Information Engineering, Tajen University, Pingtung 907, Taiwan, ROC, yjpan@mail.tajen.edu.tw