1. Department of Mathematics, Faculty of Science, University of Yaounde I, Yaounde 8390, Cameroon
2. Department of Mathematics and Physics, National Advanced School of Engineering, University of Yaounde I, UMMISCO, Team Project GRIMCAPE, LIRIMA, Yaounde 8390, Cameroon
3. Cheikh Anta Diop University, National Advanced School of Engineering, UMMISCO, 5085 Dakar, Senegal
4. Department of Mathematics and Computer Science, Faculty of Science, University of Douala, UMMISCO, Team Project GRIMCAPE, LIRIMA, Douala 24157, Cameroon
5. MaSIM Focus Area, North-West University, Mafikeng Campus, Mafikeng 2735, South Africa