Plotting results of DFT loop

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Alexandr Lozak 2019-9-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/481661-plotting-results-of-dft-loop

回答： Guru Mohanty 2020-1-13

I am trying to make multiple DFT from the code of single DFT. But cant figure out how to change plot inputs to see results as it was for single DFT.

%% Plotting single graph of DFT
va= DifVD(1:end); %DifDr(ss(1):ss(2),1);%
y = va;  %the signal you want to fft
L = length(y);
Fs=10; 
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(y,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);
% Plot single-sided amplitude spectrum.
fg=figure('Renderer', 'painters', 'Position', [100 100 700 500]);
plot(f,2*abs(Y(1:NFFT/2+1))) % semilogx(f,2*abs(Y(1:NFFT/2+1)))%
%% Plotting multiple graphs of DFT
ss=300000:6000:525158;
k=length(ss);
for i=1:k
va(:,i)= DifDr(ss(i):ss(i+1),1);
y = va;
L = length(y(1));
Fs=10; 
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y(:,i) = fft(y(:,i),NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);
% Plot single-sided amplitude spectrum.
fg=figure('Renderer', 'painters', 'Position', [100 100 700 500]);
plot(f,2*abs(Y(1:NFFT/2+1,i)))
end

How should i change last line to plot multiple results?

2 个评论
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KALYAN ACHARJYA 2019-9-23

Multiple DFT with respect to whcih parameters (In this multiple inputs)?

Alexandr Lozak 2019-9-24

在 MATLAB Online 中打开

In general it should look like

plot(f, Y(1:NFFT/2+1,i));

but i dont understand why it doesnt work for many plots

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Answer 1

Guru Mohanty 2020-1-13

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/481661-plotting-results-of-dft-loop#answer_409840

在 MATLAB Online 中打开

Hi, it is difficult to provide an exact solution without your original data. However, when I executed your code using random data, at last iteration it is trying to access beyond the last element. After modifying the loop parameter, the code should work.

clc; 
clear all; 
DifDr=randi(100,525158,5); % Demo data 
  
ss=300000:6000:525158; 
k=length(ss); 
for i=1:k-1 
va(:,i)= DifDr(ss(i):ss(i+1),1); %  
    y = va; 
    [L , ~]= size(y); 
    Fs=10;  
    NFFT = 2^nextpow2(L); % Next power of 2 from length of y 
    f = Fs/2*linspace(0,1,NFFT/2+1); 
    Y(:,i) = fft(y(:,i),NFFT)/L; 
    % Plot single-sided amplitude spectrum. 
    fg=figure('Renderer', 'painters', 'Position', [100 100 700 500]); 
    plot(f,2*abs(Y(1:NFFT/2+1,i))); % semilogx(f,2*abs(Y(1:NFFT/2+1)))% 
end 