1. Associate Professor, Dept. of Mathematics, Quaid-i-Azam Univ., Islamabad, Pakistan (corresponding author).
2. Research Associate, Dept. of Mathematics, Quaid-i-Azam Univ., Islamabad, Pakistan.
3. Professor, Dept. of Mathematics and Statistics, Luther College, Univ. of Regina, Regina, SK, Canada S4S 0A2.
4. Assistant Professor, Dept. of Basic Sciences and Humanities, College of Electrical and Mechanical Engineering, National Univ. of Sciences and Technology, Islamabad, Pakistan.