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+% spflat measures the flatness of a given spectrum
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% 
+% DESCRIPTION: spflat measures the flatness of a given spectrum using the
+% spectral flatness measure method reported in [1]. It outputs the spectral
+% flatness coefficient:
+% 
+% 0 <= sw <= 1
+% 
+% If the spectrum is peaky then sw is near 0. The more the spectrum is flat
+% the more sw in near to 1. The sw coefficient is practically calculated by
+% the ratio between geometric mean and arithmetic mean of the spectrum.
+% 
+% CALL:
+% 
+%         sw = spflat(S)
+% 
+% INPUTS:
+% 
+%         - S sample power spectrum. More than one sample spectrum can be
+%         input if they are combined in a single nxm matrix. The algorithm
+%         calculates sw for each spectrum.
+% 
+% OUTPUT:
+% 
+%         - sw spectral flatness coefficient. If more than one spectrum
+%         are input sw is a row vector. 
+% 
+% REFERENCES:
+% 
+%         [1] S. M. Kay, Modern spectral estimation:Theory and Application,
+%         Prentice Hall, Englewood Cliffs (1988) ISBN-10: 0130151599. Pages
+%         ??.
+%
+%
+%
+% VERSION:     $Id: spflat.m,v 1.2 2009/01/29 08:59:26 luigi Exp $
+%
+%
+% HISTORY:     28-01-2009 L Ferraioli
+%                 Creation
+%
+%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+function sw = spflat(S)
+  
+  % willing to work with columns  
+  [a,b] = size(S);
+  if a>1 && b>1
+    warning('Matlab:MultipleSpectra','A matrix of data was input; Spectral Flatness Coefficient will be calculated for each column')
+  else
+    if a<b
+      S = S.';
+    end
+  end
+  Ns = size(S,1);
+  gmean = exp(sum(log(S))./Ns);
+  sw = gmean./mean(S);
+  
+end
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