^pof;
Mathematics;
and;
Statistics,;
Hcbei;
University;
of;
Economics;
and;
Business,;
Hcbci;
050061,;
P.;
R.;
China;
^pof;
Applied;
Mathematics;
and;
Mechanics,;
Ordnance;
Engineering;
College,;
Hebei;
050003,;
P.;
R.;
China;