Institution: | 1. Department of Applied Mathematics,University of Information Engineering,P. O. Box 1001-747,Zhengzhou 450002,China;College of Mathematical and Information Sciences,Henan University,Kaifeng 475001,China 2. College of Mathematical and Information Sciences,Henan University,Kaifeng 475001,China 3. Department of Mathematics,Beijing Normal University,Beijing 100875,China |