Error while using transfer function 'tf'

I tried different inputs as numerator and denominator to create a transfer function using 'tf' command, but my MATLAB leaves this message everytime: 'Incorrect number or types of inputs or outputs for function 'tf''. And this exact code runs perfectly in online MATLAB FYI. Any help is appreciated!

theta_hat = [-1.77627176214971;0.790085804375558;-0.0407175636083817;0.0479175052321617];
a1 = theta_hat(1); a2 = theta_hat(2); b0 = theta_hat(3); b1=theta_hat(4);
num=[b0 b1];den=[1 a1 a2];gz = tf(num,den);

Answer 1

[Sam Chak]

Hi @Keerthik Dhivya

Please check if you have a user-defined function m-file with the same name as 'tf' that is saved in the current path.

which -all tf

/MATLAB/toolbox/control/ctrlmodels/@tf/tf.m                 % tf constructor
/MATLAB/toolbox/control/ctrlmodels/@DynamicSystem/tf.m      % DynamicSystem method
/MATLAB/toolbox/ident/ident/@idParametric/tf.m              % idParametric method
/MATLAB/toolbox/mpc/mpc/@mpc/tf.m                           % mpc method
/MATLAB/toolbox/shared/controllib/engine/@StaticModel/tf.m  % StaticModel method

[Keerthik Dhivya]

Please find the attached result i have got in command window here:

[Sam Chak]

Thanks @Keerthik Dhivya, I see it now. It appears that the Control System Toolbox is not installed. The 'tf' function from the Control System Toolbox is necessary to represent linear dynamical systems in transfer function form. This likely explains why it returns the error message 'Incorrect number or types of inputs or outputs for function tf'.

Go to the Add-Ons manager to install the Control System Toolbox:

https://www.mathworks.com/help/matlab/matlab_env/get-add-ons.html

[Keerthik Dhivya]

I installed control system toolbox, now its working well.

Thanks for your timely help! @Sam Chak

[Sam Chak]

You're welcome, @Keerthik Dhivya. Feel free to post a new question if you encounter the control design problem. The plant gz(s) is unstable.

theta_hat = [-1.77627176214971;0.790085804375558;-0.0407175636083817;0.0479175052321617];
a1 = theta_hat(1); a2 = theta_hat(2); b0 = theta_hat(3); b1=theta_hat(4);
num=[b0 b1]; den=[1 a1 a2]; gz = tf(num,den)

gz =
 
   -0.04072 s + 0.04792
  ----------------------
  s^2 - 1.776 s + 0.7901
 
Continuous-time transfer function.

step(gz)

[Keerthik Dhivya]

Sure, thanks again!

[joseph timoney]

Hi, did you find an answer to this. I have the exact same problem. It just won't work in the desktop version and I don't have any other m-files withe the same name, Thanks, Joe

[Walter Roberson]

@joseph timoney

What code are you executing, and what error message are you getting?

Do you have the Control System Toolbox installed and licensed?

[Sam Chak]

@joseph timoney, please type this and report what you see on the status output and the errmsg output:

[status, errmsg] = license('checkout', 'Control_Toolbox')

[joseph timoney]

Hi Sam it says

[status, errmsg] = license('checkout', 'Control_Toolbox')

status =

1

errmsg =

0×0 empty char array

I have a sitewide license with my institution. Let me know what you think, thanks,

[Sam Chak]

If you get exactly the same error message, "Incorrect number or types of inputs or outputs for function 'tf'", can you show the full code so that we can test it out?

[joseph timoney]

numerator = 1;

denominator = [2,3,4];

sys = tf(numerator,denominator)

"Incorrect number or types of inputs or outputs for function 'tf'."

Is there a conflict beteen tf in the signal processing toolbox and tf in the control toolbox?

[Dyuman Joshi]

That code checks whether a particular item is licensed or not.

Type "ver" in the command window and see if the Control System Toolbox is installed or not.

[Sam Chak]

@joseph timoney, If the Control System Toolbox is installed in your machine, you should see the tf.m file under the control folder. Also use ver as advised by @Dyuman Joshi.

ver

-----------------------------------------------------------------------------------------------------
MATLAB Version: 23.2.0.2436196 (R2023b) Update 4
MATLAB License Number: 0
Operating System: Linux 5.4.233-0504233-generic #202302250651 SMP Sat Feb 25 12:26:27 UTC 2023 x86_64
Java Version: Java 1.8.0_292-b10 with AdoptOpenJDK OpenJDK 64-Bit Server VM mixed mode
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