1. Department of Mathematics and Statistics, Zhoukou Normal University, Zhoukou, Henan 466001, P. R. China
2. Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario Canada, N2L 3G1, Canada
3. Department of Applied Mathematics, Northwestern Polytechnical University, Xi’an, Shaanxi, 710072, P. R. China
4. Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario Canada, N2L 3G1, Canada
5. College of Computer Science and Engineering, Chongqing University of Technology, Chongqing 400054, P. R. China