1. Department of Mathematics, Faculty of Liberal Arts, Rajamangala University of Technology Rattanakosin, Samphanthawong, Bangkok 10100, Thailand
2. Institute of Research and Development, Rajamangala University of Technology Rattanakosin, 96 Mu 3 Phutthamonthon Sai 5 Raod, Salaya, Phutthamonthon, Nakhon Pathom 73170, Thailand