[1] COMSATS Univ Islamabad, Dept Math, Lahore Campus, Lahore, Pakistan
[2] King Faisal Univ, Al Hufuf, Saudi Arabia
[3] Univ Lahore, Dept Math, Gujrat Campus, Gujrat, Punjab, Pakistan
[4] Univ Putra Malaysia, Fac Engn, Dept Aerosp Engn, Serdang, Malaysia