[1] SVEC, Dept Math, Tirupati 517502, Andhra Pradesh, India
[2] VIT Univ, Dept Math, SAS, Vellore, Tamil Nadu, India
[3] Motilal Nehru Natl Inst Technol Allahabad, Dept Math, Prayagraj 211004, Uttar Pradesh, India
[4] Air Force Inst Technol, Dept Aeronaut & Astronaut, Dayton, OH 45433 USA
[5] SV Univ, Dept Math, Tirupati, Andhra Pradesh, India