离散傅立叶变换在matlab中的数据？

Question

我在时域有一些数据，每个元素之间的时间间隔是dt，我的数据是从0到N * dt秒，我希望看到我的数据从.6e15 Hz到1e15 Hz的频谱，我该怎么办？

Answer 1

下面是代码，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)); 

此代码计算傅立叶在150E-9M T0的范围变换实施例的500E-9M

Answer 2

让我们说你已经有了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));