1. School of Computer, Statistical and Mathematical Sciences, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom 2531, South Africa
2. DST-NRF Centre of Excellence in Mathematical and Statistical Sciences, Johannesburg, South Africa
3. School of Computer Science and Applied Mathematics, University of the Witwatersrand, Johannesburg, Wits 2050, South Africa