1. Department of MathematicsBharathiar UniversityCoimbatore641 046India
2. Department of MathematicsSungkyunkwan UniversitySuwon440‐746South Korea
3. Department of MathematicsAnna University Regional CampusCoimbatore641 046India
4. School of Electrical EngineeringChungbuk National University1 Chungdae‐roCheongju28644South Korea