Affiliation: | a Solution Development Department II, Fujitu Limited, 1-6-1 Marunouchi Center Building, Chiyoda-ku, Tokyo 100-8211, Japan b Department of Mathematical Sciences, Waseda University, 3-4-1 Ohkubo Shinjuku-ku, Tokyo 169-8555, Japan c Department of Mathematical Information Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan |