First Author:   Eric Kamwa Université des Antilles, LC2S UMR CNRS 8053, F-97275 Schoelcher Cedex, France eric.kamwa@univ-antilles.fr         Second Author: Ruffin-benoit Mpoy Ngoie Mathematics and Informatics Department, ISP Mbanza-Ngungu, Democratic Republic of Congo benoitmpoy@hotmail.com         Third Author: Berthold Ulungu Institut Supéerieur des Techniques Appliquées, Section Mécanique, Democratic Republic of Congo. ulungu.berthold@gmail.com