Function 'subindex' is not defined for values of class 'ss' of 'zpk'

Dear All

I am following MATLAB tutorial in Mathworks "Designing PID for Disturbance Rejection with PID Tuner" While following this tutorial, I got the following error in the picture. and another error is

"Function 'subsindex' is not defined for values of class 'zpk'."

The errors occurred after the following commands

G = zpk(-5,[-1 -2 -3 -4],6,'OutputDelay',1);
G.InputName = 'u';
G.OutputName = 'y';
C = pid(0.64362,0.30314);
C.InputName = 'e';
C.OutputName = 'u';
b = 0.7;
% The following code constructs an ISA-PID from F and C

F = tf([b*C.Kp C.Ki],[C.Kp C.Ki]);
F.InputName = 'r';
F.OutputName = 'uf';
Sum = sumblk('e','uf','y','+-');
ISAPID = connect(C,F,Sum,{'r','y'},'u');
tf(ISAPID)

% Closed-loop system with PI controller for reference tracking

sys1 = feedback(G*C,1);

% Closed-loop system with ISA-PID controller

sys2 = connect(ISAPID,G,{'r','u'},'y');

% Compare responses

step(sys1,'r-',sys2(1),'b.');
legend('show','location','southeast')
title('Reference Tracking')

The link of the tutorial is : https://www.mathworks.com/help/control/examples/designing-pid-for-disturbance-rejection-with-pid-tuner.html

Can anyone guide me how to remove these errors ?

Thank you

Answer 1

[Steven Lord]

If you run these lines of code one by one, on which line does the error occur?

My suspicion is that you have created a variable named connect if the error occurs on the line of code where you're trying to call the connect function.

[Barkat]

Thank you, Sir, The response is now correct and the codes are working.