Institution: | a Department of Applied Mathematics, Faculty of Engineering, Kobe University, Kobe, 657-8501, Japanf1naito@cs.kobef1b Department of Mathematics, Osaka University, Toyonaka, 560-0043, Japanc Division of Mathematical and Information Sciences, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, 739-8521, Japan |