--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/m-toolbox/classes/+utils/@math/dft.m	Wed Nov 23 19:22:13 2011 +0100
@@ -0,0 +1,41 @@
+% DFT Compute discrete fourier transform at a given frequency
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% DFT Compute discrete fourier transform at a given frequency
+% It is defined as 
+% X(f) = T*sum(x(t)*exp(-1i.*2.*pi.*f.*T.*t))|t=0,...,N-1
+% where T is the sampling time
+% 
+% CALL 
+% 
+% Gf = utils.math.dft(gt,f,T)
+% 
+% INPUT
+% 
+% - gt, input data series, Nx1 double
+% - f, a frequency point in Hz, 1x1 double
+% - T, sampling time in seconds, 1x1 double
+% 
+% REFERENCES
+% 
+% D. B. Percival and A. T. Walden, Spectral Analysis for Physical
+% Applications (Cambridge University Press, Cambridge, 1993) p 108.
+% 
+% L Ferraioli 09-03-2011
+%
+% $Id: dft.m,v 1.2 2011/03/29 15:36:43 luigi Exp $
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+function Gf = dft(gt,f,T)
+  
+  [nn,mm] = size(gt);
+  if nn<mm % willing to work with columns
+    gt = gt.';
+  end
+  N = numel(gt);
+  t = 0:N-1;
+  
+  ar = exp(-1i.*2.*pi.*f.*T.*t);
+  
+  Gf = T*(ar*gt);
+
+
+end
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