1Department of Mathematics, Faculty of Science and Technology Keio University Hiyoshi 3-14-1, Kohoku-ku, Yokohama, 223-8522, Japan
2Infrastructure Information Systems Division Oki Electric Industry Co.,Ltd. Shibaura 4-10-3, Minato-ku, Tokyo 108-8551, Japan
3Department of Mathematics, Faculty of Science and Technology Keio University Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522, Japan