1. Department of Applied Mathematics, National Chung Hsing University, Taichung 40249, Taiwan
2. Department of Mathematics, National Taiwan Normal University, Taipei 11677, Taiwan
3. Department of Mathematics, National Cheng Kung University, Tainan City 701, Taiwan
4. Graduate School of Informatics, Kyoto University, Japan
5. Division of Preparatory Programs for Overseas Chinese Students, National Taiwan Normal University, New Taipei City 24449, Taiwan