離散傅立葉變換在matlab中的數據？

Question

我在時域有一些數據，每個元素之間的時間間隔是dt，我的數據是從0到N * dt秒，我希望看到我的數據從.6e15 Hz到1e15 Hz的頻譜，我該怎麼辦？

Answer 1

下面是代碼，我需要：

NT=10000;%size of data that I have 
ddx=2e-9; 
dt=ddx/(3e8);%time separation between each element 
i=sqrt(-1); 
NFREQS=1000;%size of frequency array 
lambdai=150e-9; 
lambdaf=500e-9; 
freqi=3e8/lambdai;%lower limit of frequency 
freqf=3e8/lambdaf;%upper limit of frequency 
freq=zeros(1,NFREQS); 
for j=1:NFREQS 
freq(j)=freqi-j*(freqi-freqf)/NFREQS;%frequency array 
end 
arg=2*pi*freq*dt; 
lambda=linspace(lambdai,lambdaf,NFREQS); 
    for n=1:NFREQS 
    for j=1:NT 
    Exf(n)=Exf(n)+Ex(j)*exp(-i*arg(n)*j);%Ex the data that I have and Exf is fft of it 
    end 
    end 

plot(lambda,real(Epsilon)); 

此代碼計算傅立葉在150E-9M T0的範圍變換實施例的500E-9M

Answer 2

讓我們說你已經有了x。

x%is given 
fmin = 1e15; 
fmax = 6*fmin; 
numOfSamples = length(x); 
f = linspace(fmin,fmax,numOfSamples); 
t = 1 : numOfSamples; 
y=fft(x); 
plot(fftshift(y));