Tian Qin WANG College of Computer Science and Information Engineering,He'nan University, Kaifeng 475001,P.R.China Institute of Data and Knowledge Engineering,He'nan University,Kaifeng 475001,P.R.China
Acta Mathematica Sinica, Chinese Series
.
2009, (02): 11
-22
.
DOI: 10.12386/A2009sxxb0026
