1. African Center of Excellence in Data Science, University of Rwanda, Kigali P.O. Box 4285, Rwanda
2. Department of Information Engineering Computer Science and Mathematics, University of l’Aquila, 56121 Pisa, Italy
3. Department of Applied Statistics, University of Rwanda, Kigali P.O. Box 4285, Rwanda
4. Department of Mathematics, College of Science and Technology, University of Rwanda, Kigali P.O. Box 3900, Rwanda
5. Department of Mathematical Sciences and Global Studies, Bentley University, Watham, MA 02452-4705, USA
6. Department of Mathematical Sciences and Global Studies, Université Paris 1 (SAMM), 75634 Paris, France
7. Department of Mathematical Sciences and Global Studies, Université Toulouse 1 (TSE-R), 31042 Toulouse, France