Mathematical Theory and Applications ›› 2017, Vol. 37 ›› Issue (1): 1-6.
Liu Zhongyun1 ,Wu Nianci 1 ,Qin Xiaorong1 ,Zhang Yulin2
1.School of Mathematics and Statistics,Changsha University of Science and Technology,Changsha 410004,China; 2.Centro de Matema′tica,Universidade do Minho,4710-057Braga,Portugal