1. Naveen Jindal School of Management, University of Texas at Dallas, Richardson, TX 75080-3021 USA.
2. School of Data Science, City University of Hong Kong, Kowloon, Hong Kong SAR.
3. Department of Statistics, Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR.
4. Department of Mathematics, City University of Hong Kong, Kowloon, Hong Kong SAR.