1. School of Mathematics and Statistics, Northwestern Polytechnical University 1 , Xi’an 710072, China
2. School of Mathematics and Statistics, Ningxia University 2 , Yinchuan, 750021, China
3. MOE Key Laboratory for Complexity Science in Aerospace, Northwestern Polytechnical University 3 , Xi’an 710072, China
4. School of Mathematical Sciences, Shanxi University 4 , Taiyuan, 0300062, China