[1] King Khalid Univ, Coll Sci, Dept Math, Abha, Saudi Arabia
[2] Quaid I Azam Univ, Dept Math, Islamabad 44000, Pakistan
[3] Univ Birmingham, Dept Civil Engn, Birmingham, W Midlands, England
[4] GITAM Univ, Dept Math, Nagadenahalli, Karnataka, India