1. School of Mathematics and Statistics , Xi’an Jiaotong University, 710049 Xi’an , P R China
2. College of Computer Science and Technology , Xi’an University of Science and Technology, 710054 Xi’an , P R China
3. AVIC Aeronautical Laboratory of Computational Fluid Dynamics , Xi’an Aeronautics Computing Technique Research Institute, Xi’an 710068 , P R China