1. Department of Mathematics and Computer Science, Faculty of Science, University of Ngaoundéré, Ngaoundere, Cameroon
2. Department of SFTI, School of Chemical Engineering and Mineral Industries, University of Ngaoundéré, Ngaoundere, Cameroon
3. Department of Mathematics, Rhodes University, Grahamstown, South Africa
4. College of Engineering and IT, University of Dubai, Dubai, United Arab Emirates