About the Authors

Rui Fan

Affiliation State Key Laboratory of Software Development Environment, Beihang University, Beijing, P. R. China

Jichang Zhao

Affiliation School of Economics and Management, Beihang University, Beijing, P. R. China

Yan Chen

Affiliation State Key Laboratory of Software Development Environment, Beihang University, Beijing, P. R. China

Ke Xu

kexu@nlsde.buaa.edu.cn

Affiliation State Key Laboratory of Software Development Environment, Beihang University, Beijing, P. R. China

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Performed the experiments: RF JZ YC. Analyzed the data: RF JZ YC. Wrote the paper: JZ KX. Designed the experiments: JZ RF KX. Prepared the figures: RF JZ YC.