1. Department of Bioscience and Bioinformatics, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka, 820--8502, Japan.
2. Department of Information Science and Engineering, Ritsumeikan University, Kusatsu, 525--8577, Japan.
3. Graduate School of Advanced Science Engineering, Hiroshima University, Higashihiroshima, 739--8527 Japan.