Qiang LIU College of Applied Sciences,Beijing University of Technology,Beijing 100124,P.R.China School of Statistics,Capital University of Economics and Business,Beijing 100070,P.R.China Liu Gen XUE Fang CHEN College of Applied Sciences,Beijing University
Acta Mathematica Sinica, Chinese Series
.
2009, (03): 135
-146
.
DOI: 10.12386/A2009sxxb0066
