Graphical interpretation of magnitude (derived from fft)

1 次查看（过去 30 天）

显示更早的评论

Pedro Mateus 2014-3-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/120119-graphical-interpretation-of-magnitude-derived-from-fft

关闭： MATLAB Answer Bot 2021-8-20

在 MATLAB Online 中打开

Hello to all users of Matlab.

I have 20 years of temperature measurements. Twice a day (max and min) with 12 hours between measurements. To understand which frequencies are more pronounced, I applied the following code:

x = detrend(x);                    
n = length(x);               
nfft = 2^nextpow2(n);
Fs = 1/(12*60*60);             
f = 0 : Fs/(nfft-1) : Fs/2;
Y = fft(x, nfft);           
Y = Y(1:((nfft+1)/2));
Y = Y/(nfft/2);
Ya = abs(Y);            
figure(100)
plot(f, Ya); xlabel('Frequency (Hz)'); ylabel('|Y(f)|'); grid on

I get:

The energy is concentrated in the last frequency (Nyquist, if I'm not mistaken). Is there any error in the code? Not the first time I do this, but never for this type of data and with a sample rate (Fs) so small.

Thanks for the help