1. Department of Mathematics , Government College University , Lahore 54000 , Pakistan ; Department of Mathematics and Applied Mathematics , University of Pretoria , Pretoria 0002 , South Africa
2. Department of Sciences and Humanities , National University of Computer and Emerging Sciences , Lahore Campus, Pakistan
3. Institute of Research and Development of Processes , University of the Basque Country , Campus of Leioa (Bizkaia) - P.O. Box 644- Bilbao , Barrio Sarriena, 48940- Leioa, Spain ;