compute_fft.m

主成分分析和偏最小二乘SquaresPrincipal成分分析（ PCA ）和偏最小二乘（ PLS ）

function [f,mag]=compute_fft(time,data,action);
% CUMPUTE_FFT compute FFT for vector 'data'
% action: 'plot' , 'noplot'
%
% last modified 15.12.04


xfft = 2/length(data)*fft(data);

xfft(xfft == 0) = 1e-17;

% Compute magnitude, dB
mag = 20*log10(abs(xfft(1:ceil(length(data)/2),:)));
if std(diff(time))>=1e-7
    disp('Warning! Sample rate is not constant. FFT may be invalid.');
end
Fs=1/mean(diff(time));
f = (0:length(mag)-1)*Fs/length(data);
if strcmp(lower(action),'plot')
	plot(f,mag); grid on;
	ylabel('Magnitude, (dB)');
	drawnow;
end