Affiliation: | a Unité associée au CNRST (Maroc), URAC 02, Morocco b UMI, UMMISCO (IRD, UPMC), France c Laboratory of MDP, University Cadi Ayyad, Faculty of Sciences, Department of Mathematics, B.P. 2390 Marrakesh, Morocco d University Cadi Ayyad, Faculty of Sciences Semlalia, Department of Mathematics, B.P. 2390 Marrakesh, Morocco |