1. Department of Mathematics, Allama Iqbal Open University, H-8 , Islamabad , Pakistan
2. Electrical Engineering Department, College of Engineering, Princess Nourah bint Abdulrahman University , P. O. Box 84428 , Riyadh 11671 , Saudi Arabia
3. Department of Mathematics, King Abdulaziz University , P.O. Box 80203 , Jeddah 21589 , Saudi Arabia