1. School of Computational and Communication Science and Engineering, The Nelson Mandela African Institution of Science and Technology (NM-AIST), P.O. Box 447, Arusha, Tanzania
2. Department of Mathematics, Humanities and Social Science (MHSS), National Institute of Transport (NIT), P.O. Box 705, Dar-es-Salaam, Tanzania
3. Institute of Mathematical Science, Strathmore University, Nairobi, Kenya
4. Department of Biometry and Mathematics, Botswana University of Agriculture and Natural Resources, Private Bag 0027, Gaborone, Botswana