1. Department of Mathematics, Faculty of Science, King Mongkut's University of Technology Thonburi, Bangkok 10140, Thailand
2. Program of Mathematics, Faculty of Science, Ubon Ratchathani Rajabhat University, Ubon Ratchathani 34000, Thailand
3. Department of Mathematics and Statistics, University of Swat, Swat 19120, Khyber Pakhtunkhwa, Pakistan