Yong Liang HUO College of Mathematical and Statistics,Chongqing University of Arts and Sciences, Yongchuan 402160,P.R.China San Yang LIU Department of Applied Mathematics,Xidian University,Xi'an 710071,P.R.China
Acta Mathematica Sinica, Chinese Series
.
2009, (05): 81
-88
.
DOI: 10.12386/A2009sxxb0113
