An example [appears][1] in : S. Chen, G. Liu, S. Xin, Y. Zhou, Y. He, C. Tu, *Algebraic equation of geodesics on the 2D Euclidean space with an exponential density function* 
**Communications in Information and Systems**
Volume 18 (2018)
Number 2


  [1]: http://dx.doi.org/10.4310/CIS.2018.v18.n2.a2