1. Department of Mathematics, National University of Modern Languages, Main Campus, H9 Islamabad 44000, Pakistan
2. Department of Physics, Zhejiang Normal University, Jinhua 321004, P. R. China
3. Department of Mathematics, COMSATS University Islamabad, Lahore Campus, Lahore, Punjab, Pakistan
4. Department of Mathematics, COMSATS University Islamabad, Sahiwal Campus, Sahiwal, Punjab, Pakistan