Affiliation: | 1. Department of Applied Mathematics, Nanjing Forestry University, Nanjing 210037, PR China;2. Department of Mathematics, Hokkaido University, Sapporo 060-0810, Japan;3. Department of Mathematics, Southeast University, Nanjing 210096, PR China;4. School of Mathematics and Computational Science, Hunan University of Science and Technology, Xiangtan 411201, PR China |