Affiliation: | 1. Department of Mathematics, Faculty of Science and Engineering, Walter Sisulu University, Private Bag X1, Mthatha 5117, Republic of South Africa;2. School of Mathematical Sciences, Howard College, University of KwaZulu‐Natal, Durban 4041, Republic of South Africa;3. School of Statistics and Actuarial Science, Howard College, University of KwaZulu‐Natal, Durban 4041, Republic of South Africa |