1. Assistant Professor, Dept. of Mathematics, Quaid-i-Azam Univ., 45320, Islamabad 44000 Pakistan (corresponding author).
2. Associate Professor, Dept. of Mathematics, Quaid-i-Azam Univ., 45320, Islamabad 44000 Pakistan.
3. Professor, Dept. of Mathematics, Quaid-i-Azam Univ., 45320, Islamabad 44000 Pakistan; and Dept. of Physics, Faculty of Science, King Saud Univ. P.O. Box 1846, Riyadh 11321, Saudi Arabia.
4. Professor, Dept. of Physics, Faculty of Science, King Saud Univ., P.O. Box 1846, Riyadh 11321, Saudi Arabia.