# Help With for loop with tranfer function and step

3 views (last 30 days)
Davide Cannavacciuolo on 20 Nov 2023
Commented: Sam Chak on 20 Nov 2023
s=tf('s');
G=1/(s^2+0.4*s+0.1);
K=[1 2 3 4 5 6];
figure
hold on
for i=1:1:length(K)
T=K(i)*G;
step(T)
S=stepinfo(T);
L=S.Peak(T)
end
I have this code but i get the error : "Unable to use a value of type tf as an index."
I want actually to make a vector containg all the values of the peak values and only then plot the peaks with the corresponding value of gain.
Thank you in advance

Sam Chak on 20 Nov 2023
You probably want to plot like this:
s = tf('s');
G = 1/(s^2 + 0.4*s + 0.1);
K = [1 2 3 4 5 6];
figure(1)
hold on
for i = 1:length(K)
T = K(i)*G;
step(T)
S = stepinfo(T);
L(i) = S.Peak;
end
grid on
hold off
figure(2)
plot(K, L, '-o'), grid on
xlabel('Gain'), ylabel('Peak')
##### 2 CommentsShow NoneHide None
Davide Cannavacciuolo on 20 Nov 2023
Thank you so much!
Sam Chak on 20 Nov 2023
Ciao @Davide Cannavacciuolo. You're welcome!

### More Answers (1)

Dyuman Joshi on 20 Nov 2023
Edited: Dyuman Joshi on 20 Nov 2023
There is no field in the struct 'S' with name 'T'. Thus you get the error in the line you defined 'S'.
I suspect that you want to get the 'Peak' value for each system -
s=tf('s');
G=1/(s^2+0.4*s+0.1);
K=[1 2 3 4 5 6];
%Preallocation
L = K.*0;
figure
hold on
for i=1:1:length(K)
T=K(i)*G;
step(T);
S=stepinfo(T);
L(i)=S.Peak;
end
L
L = 1×6
10.7689 21.5379 32.3068 43.0757 53.8447 64.6136
Davide Cannavacciuolo on 20 Nov 2023
Thank you so much!

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