YAN-PING LI1, LAI-FENG LU1,2,+ AND KAI ZHANG1
1School of Mathematics and Information Science
Shaanxi Normal University
Xi'an, 710119 P.R. China
2Guizhou Provincial Key Lab. of Public Big Data
GuiZhou University
Guiyang, 550025 P.R. China
E-mail: {lyp; lulaifeng}@snnu.edu.cn; 629zhangkai@163.com