[1] Yokohama Natl Univ, Grad Sch Environm & Informat Sci, Yokohama, Kanagawa, Japan
[2] Hiroshima Coll, Natl Inst Technol, Hiroshima, Japan
[3] Konkuk Univ, Dept Math Educ, Seoul, South Korea
[4] Yokohama Natl Univ, Fac Environm & Informat Sci, Yokohama, Kanagawa, Japan