1. College of Mathematics and Statistics, North China University of Water Resources and Electric Power, Zhengzhou 450011, China
2. Department of Mathematics and Information Science, Henan Normal University, Xinxiang, 453007, China
3. Laboratoire de Mathématiques et Applications, UMR CNRS 7348-SP2MI, Université de Poitiers, Boulevard Marie et Pierre Curie-Téléport 2 86962, Chasseneuil Futuroscope Cedex, France