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bugfix DFT_time2freq.m

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The DFT used to operate on absolute time. This is now fixed.
This commit is contained in:
Sebastian Held 2010-07-14 10:23:55 +02:00
parent fb164ba1fe
commit 0d2811ff21
2 changed files with 20 additions and 1 deletions
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18
matlab/DFT_time2freq.m
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@ -1,12 +1,28 @@
function f_val = DFT_time2freq( t, val, freq ) function f_val = DFT_time2freq( t, val, freq )
% val = FFT_time2freq( t, val, freq ) % f_val = DFT_time2freq( t, val, freq )
% %
% computes the DFT at the given frequencies % computes the DFT at the given frequencies
% f_val: single-sided spectrum
%
% example:
% t=linspace(0,1,100);
% t_val=0.9*sin(2*pi*3*t); % sine wave; amplitude 0.9; frequency 3 Hz
% f=linspace(1,5,101);
% f_val=DFT_time2freq( t, t_val, f );
% interp1(f,abs(f_val),3)
% ans = 0.8910
% plot( t, t_val )
% plot( f, abs(f_val) )
%
% See also FFT_time2freq
if numel(t) ~= numel(val) if numel(t) ~= numel(val)
error 'numel(t) ~= numel(val)' error 'numel(t) ~= numel(val)'
end end
% convert absolute time into relative time
t = t - t(1);
f_val = zeros(1,numel(freq)); f_val = zeros(1,numel(freq));
for f_idx=1:numel(freq) for f_idx=1:numel(freq)
f_val(f_idx) = sum( val .* exp( -1i * 2*pi*freq(f_idx) * t ) ); f_val(f_idx) = sum( val .* exp( -1i * 2*pi*freq(f_idx) * t ) );

3
matlab/FFT_time2freq.m
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@ -1,4 +1,7 @@
function [f,val] = FFT_time2freq( t, val ) function [f,val] = FFT_time2freq( t, val )
% [f,val] = FFT_time2freq( t, val )
%
% See also DFT_time2freq
dt=t(2)-t(1); % timestep dt=t(2)-t(1); % timestep
L=numel(val); % signal length L=numel(val); % signal length