1. School of Mathematics and Statistics, Beijing Key Laboratory on MCAACI Beijing Institute of Technology Beijing P.R. China
2. School of Mathematics and Statistics Northwestern Polytechnical University Xi'an Shaanxi P.R. China
3. Department of Mathematics European Centre of Excellence NTIS ‐ New Technologies for the Information Society University of West Bohemia Pilsen Czech Republic
4. School of Mathematics and Statistics Henan University Kaifeng P.R. China