NDFT for nonequispaced data either in time and frequency domain

the algorithms written by Tobias Knopp 
based on the paper
Potts, D., Steidl G., and Tasche M.
 Fast Fourier transforms for nonequispaced data: A tutorial.
 in: Modern Sampling Theory: Mathematics and Applications, 
 J.J. Benedetto and P. Ferreira (Eds.), Chapter 12, pages 249-274. 1998

Available from:
http://www.math.uni-luebeck.de/potts
 
