Derivatives of Generalized Distance Functions and Existence of Generalized Nearest Points.

Chong Li Renxing Ni Derivatives of Generalized Distance Functions and Existence of Generalized Nearest Points. 44-55 2002 115 Journal of Approximation Theory 1 http://dx.doi.org/10.1006/jath.2001.3651 db/journals/jat/jat115.html#LiN02