How can I plot the fast Fourier transform of a given step response

How can I plot the fast Fourier transform of a given step response as shwon in the atatched code & picture

And here is my code

clear; clc;close all;
s= tf('s');
num=1;
den=s*(s/10+1);
G= num/den;
H=1;

K2=sqrt(10);  %K2       
G2=G*K2;
closed_system2=feedback(G2,H);
step(closed_system2,H,'r');
hold on 

K3=10;        %K3
G3=G*K3;
closed_system3=feedback(G3,H);
step(closed_system3,H,'b'); 
grid on

title('Response to a refrence step input');
legend('step input @k=10^0.5','step input @k=10')

Answer 1

[Milan Padhiyar]

Hello,

To plot a fast Fourier transform of the step response, first, you need to store the signal values.

Please find below command to store the output from the “step” command,

% y is the step response signal array and tOut represent the time array
[y,tOut] = step(sys)

Please find the following documents that show how to use “fft” command to find the fast Fourier transform and how to plot that.

https://in.mathworks.com/help/matlab/ref/fft.html

https://in.mathworks.com/matlabcentral/answers/36430-plotting-the-frequency-spectrum

I hope this help you to resolve your query.

Thanks