1. School of Mathematics, Statistics and Computer Science , University of KwaZulu-Natal , Durban , South Africa DSI-NRF Center of Excellence in Mathematical and Statistical Sciences (CoE-MaSS)
2. Department of Mathematics and Applied Mathematics , Sefako Makgatho Health Sciences University , P. O. Box Medunsa , Pretoria , South Africa
3. School of Mathematics, Statistics and Computer Science , University of KwaZulu- Natal , Durban , South Africa