Error Using Plot for a Derived Fourier Transform Signal

Question

Mohammed Alsubhi 2020-8-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/574780-error-using-plot-for-a-derived-fourier-transform-signal

评论： Sriram Tadavarty 2020-8-4

I derived the Fourier Transform of a signal analytically, and I am trying to plot its magnitude with respect to frequency. However, I keep getting the following error "Vectors must be the same length". I tried using linspace but I am not sure if I implemented it correctly.

clc;
BW=3000;                                                            
Fs=2*BW;                                                            
Ts=1/fs;                                                                   
Tend=3;                                                              
Tend=ceil(Tend/Ts)*Ts;                                                        
N=(Tend/Ts)+1;                                                                
To=N*Ts; 
Fo=1/To;
t=(0:Ts:(N-1)*Ts);                                                                   
Freq=(-Fs/2:Fo:Fs/2-Fo);
G1=3*10^-3.*sinc(pi*f/1000).^2.*exp(-1i*pi*f/125);
G2=3*10^-3.*sinc(pi*f/2000).^2.*exp(-1i*pi*f/225);
Gf_Derived=(G1-G2);
figure(1)
plot(Freq,abs(Gf_Derived),'Linewidth',2)
grid on

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Answer 1

Sriram Tadavarty 2020-8-4

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Hi Mohammed,

The code that is provided as some variable issues. I tried to correct and placed the code here, based on what u r trying to do.

The error you observe is due to the length of Freq and Gf_Derived, not being the same. In order to use plot, both the input lengths Freq and Gf_Derived must be the same.

Look over the modified code below:

clc;
BW=3000;                                                            
Fs=2*BW;                                                            
Ts=1/Fs;
Tend=3;                                                              
Tend=ceil(Tend/Ts)*Ts;                                                        
N=(Tend/Ts)+1;                                                                
To=N*Ts; 
Fo=1/To;
t=(0:Ts:(N-1)*Ts);                                                                   
Freq=(-Fs/2:Fo:Fs/2-Fo);
G1=3*10^-3.*sinc(pi*Freq/1000).^2.*exp(-1i*pi*Freq/125);
G2=3*10^-3.*sinc(pi*Freq/2000).^2.*exp(-1i*pi*Freq/225);
Gf_Derived=(G1-G2);
figure(1)
plot(Freq,abs(Gf_Derived),'Linewidth',2)
grid on