Affiliation: | 1. College of Mathematics and Systems Science, Shandong University of Science and Technology, Qingdao 266590, China2. Department of Mathematics, Linyi University, Linyi 276005, China3. School of Mathematical Sciences, Qufu Normal University, Qufu 273100, China4. Department of Computer Science, The University of Suwon, Wau-ri, Bongdam-eup, Hwaseong-si, Gyeonggi-do, 445-743, Korea |