1. Mathematics Department, Faculty of Science and Technology, Universitas Islam Negeri Syarif Hidayatullah Jakarta, Jl. Ir. H. Juanda No. 95, Ciputat 15412, Indonesia
2. Graduate School of Informatics and Engineering, The University of Electro-Communications, 5-1 Chofugaoka 1-chome, Chofu, Tokyo 182-8585, Japan