33 lines
777 B
Matlab
33 lines
777 B
Matlab
function f_val = DFT_time2freq( t, val, freq )
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% f_val = DFT_time2freq( t, val, freq )
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%
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% computes the DFT at the given frequencies
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% f_val: single-sided spectrum
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%
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% example:
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% t=linspace(0,1,100);
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% t_val=0.9*sin(2*pi*3*t); % sine wave; amplitude 0.9; frequency 3 Hz
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% f=linspace(1,5,101);
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% f_val=DFT_time2freq( t, t_val, f );
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% interp1(f,abs(f_val),3)
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% ans = 0.8910
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% plot( t, t_val )
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% plot( f, abs(f_val) )
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%
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% See also FFT_time2freq
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if numel(t) ~= numel(val)
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error 'numel(t) ~= numel(val)'
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end
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% convert absolute time into relative time
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t = t - t(1);
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f_val = zeros(1,numel(freq));
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for f_idx=1:numel(freq)
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f_val(f_idx) = sum( val .* exp( -1i * 2*pi*freq(f_idx) * t ) );
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end
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f_val = f_val / numel(t);
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f_val = f_val * 2; % single-sided spectrum
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