1. University of La Rochelle, MIA Laboratory, La Rochelle, France
2. MAIS Laboratory, MAMCS Group, Moulay Ismail University of Meknes, Errachidia, MoroccoThis paper is dedicated to the memory of Pr. Andro Mikelić. The first author had the chance to work with him. His culture, his mastery of both physical sciences and mathematics, should have given us many other results. He passed away but the admiration we feel for him remains.