Key Laboratory of Combinatorial Biosynthesis and Drug Discovery Ministry of Education and School of Pharmaceutical Sciences Wuhan University, Wuhan, China.|Department of Mathematical Sciences, University of Memphis, Memphis, TN, USA.|Department of Mathematical Sciences, University of Memphis, Memphis, TN, USA.|Institute of Statistics, National Chiao Tung University, Hsinchu, Taiwan.|Department of Biological Sciences, University of Memphis, Memphis, TN, USA.|Department of Mathematical Sciences, University of Memphis, Memphis, TN, USA.|Institute of Statistics, National Chiao Tung University, Hsinchu, Taiwan. hslu@stat.nctu.edu.tw.