Error using ^ for control systems related functions

I have a simple transfer function as shown below.

>> P = tf(8,[1 8])

P =

8

-----

s + 8

Continuous-time transfer function.

However when I attempt to use the minreal() function I encounter this error:

>> minreal(P)

Error using DynamicSystem/minreal

Incorrect dimensions for raising a matrix to a power. Check that the matrix is

square and the power is a scalar. To operate on each element of the matrix

individually, use POWER (.^) for elementwise power.

This error is not limited to the transfer function above but to more complex transfer functions as well. Additionally, I have encountered this issue when running other codes as well, notably converting state space models to a transfer function shown below.

>> A = [-1.5,-2;1,0];

B = [0.5;0];

C = [0,1];

D = 0;

sys = ss(A,B,C,D)

sys =

A =

x1 x2

x1 -1.5 -2

x2 1 0

B =

u1

x1 0.5

x2 0

C =

x1 x2

y1 0 1

D =

u1

y1 0

Continuous-time state-space model.

>> sys_as_tf = tf(sys)

Error using DynamicSystem/tf

Incorrect dimensions for raising a matrix to a power. Check that the matrix is

square and the power is a scalar. To operate on each element of the matrix

individually, use POWER (.^) for elementwise power.

Similarly when I attempt to convert a state space model to a transfer function using ss2tf I encounter the same error as well.

>> A = [-1.5,-2;1,0];

B = [0.5;0];

C = [0,1];

D = 0;

>> tfsys = ss2tf(A,B,C,D);

Error using ^

Incorrect dimensions for raising a matrix to a power. Check that the matrix is

square and the power is a scalar. To operate on each element of the matrix

individually, use POWER (.^) for elementwise power.

Error in poly (line 2)

sqrd=x^2+y;

Error in ss2tf (line 30)

den = poly(p);

I have tried reinstalling the toolbox, reinstalling MATLAB r2023a and even installed version r2022a but I am not able to resolve this error regardless of what I do. I assume it may have something to do with the laptop I am using as I do not face these issues on MATLAB Online but I am unsure of what specifically could be causing these issues locally in my device.

Answer 1

[Walter Roberson]

you have supplied your own poly.m which is interfering with using the matlab poly() function

[Mohammad Aliuddin Mohamed Anwer]

Thank you, it worked! I forgot I created an m file long ago named poly.m and after deleting it everything worked.

[Sam Chak]

@Mohammad Aliuddin Mohamed Anwer, Good to know that you fixed the issue. Thanks @Walter Roberson.

Answer 2

[Sam Chak]

Hi Aliuddin,

If you want to get the transfer function directly, then use this syntax:

tfsys = tf(ss(A,B,C,D))

[Mohammad Aliuddin Mohamed Anwer]

Thank you for the response but I still face the same issue in my initial question,

>> A = [-1.5,-2;1,0];

B = [0.5;0];

C = [0,1];

D = 0;

>> tfsys = tf(ss(A,B,C,D))

Error using DynamicSystem/tf

Incorrect dimensions for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To operate on

each element of the matrix individually, use POWER (.^) for elementwise power.

[Sam Chak]

Try fixing this one:

sqrd = x.^2 + y

[Mohammad Aliuddin Mohamed Anwer]

I assume you mean I should edit my poly() function to the add in the element-wise exponential? I tried doing that and I end up having a different error indicating I have insufficient input arguments.

>> tfsys = tf(ss(A,B,C,D))

Error using DynamicSystem/tf

Not enough input arguments.