1. Professor, Dept. of Applied Mathematics, Indian Institute of Technology (ISM), Dhanbad 826004, Jharkhand, India.
2. Dept. of Applied Mathematics, Indian Institute of Technology (ISM), Dhanbad 826004, Jharkhand, India; formerly, Assistant Professor, Dept. of Mathematics, Neotia Univ., Kolkata 743368, India (corresponding author).
3. Professor, Dept. of Mathematics, Hampton Univ., Hampton 23668, Virginia.