1. Laboratory of Applied Mathematics , Mathematics Department , University of Biskra , 07000 Biskra , Algeria
2. Laboratory of Pure and Applied Mathematics , University of Tizi-Ouzou , 15000 Tizi-Ouzou , Algeria
3. Mathematics Department , University of Biskra , 07000 Biskra ; and Research Unit LaMOS (Modeling and Optimization of Systems), University of Bejaia, 06000 Bejaia , Algeria
4. Research Unit LaMOS (Modeling and Optimization of Systems) , University of Bejaia , 06000 Bejaia , Algeria