Funding for this research was provided by:
The National Key Basic Research Program (2013CB036005)
The National Natural Science Fund Youth Project (51608529)
Article History
Received: 21 April 2018
Accepted: 21 March 2019
First Online: 30 March 2019
Compliance with Ethical Standards
:
: YX conceived, designed, and performed the study. ZX and ZW collected and analysed the example used in the paper. YX and HL wrote and revised the paper together. The authors have read, and approved, the final published manuscript.
: The authors declare no conflict of interest.
: This theoretical paper does not rely on empirical data. All of the plots can be generated by following the equations and instructions provided in the paper.