Undefined function or method 'tf' for input arguments of type 'double'.

The error message is clear: "Undefined function or method 'tf' for input arguments of type 'double'." This mean, that there is no TF function defined for doubles. Even clearing will not change this. The found @dfilt\tf function is obviously defined for dfilt objects.

The call a = tf([5],[0.8 1]) is only possible, if you have the Control System Toolbox, see: http://www.mathworks.com/help/control/ref/tf.html

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lounis chehrit 2021-6-8

Hello everyone,

I hope you're doing well.

I have an issue, can you help me on this please?

I have two signal column vectors ( input and output ) : ( very large but they both have the same size):

x_inp=[0.0001, -0.0233, ..... ]

x_out=[0.005, -0.0053, ..... ]

i also have a system TF, which is represented like this:

Real( H(s) ) = 23 cos (2*pi*s) + 12 cos (5*pi*s/10) + 1 cos (2*pi*s)/19 + 0.75 cos (5*pi*s/10).

Imag( H(s) ) =11 sin (3*pi*s) + 7 cos (9*pi*vs2) + 10 sin (2*pi*s)/2 + 1.25 sin (4*pi*s/18).

I want to know if , TF( x_out / x_inp ) = H(s).

I tried this :

sys = Real( H(s) ) + i.* Imag (H(s) ).

so to compute the TF( x_out / x_inp ) i did this :

TL1 = tf ( x_inp )

TL2 = tf ( x_out).

and then :

signal = TL2 ./ TL1.

But it doesn't work.

Can anyone please, tell me how can i compute that tf and compare them to the H(s) system.

Or is there another method to see if TF( x_out / x_inp ) = H(s) ? Wether fft method or something like that.

Thank you in advance !

Steven Lord 2021-6-8

This is not related to the original question so you should ask it as a new question using the Ask link above. When you do post that new question please clarify what "does not work" means.

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Answer 2

Azzi Abdelmalek 2013-2-12

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/63155-undefined-function-or-method-tf-for-input-arguments-of-type-double#answer_74739

编辑：Azzi Abdelmalek 2013-2-12

在 MATLAB Online 中打开

Try

clear tf
a = tf([5],[0.8 1])

% You, probably used tf as a variable in your script, or you don't have a system control toolbox

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Venkatapathi 2013-2-12

Hi azzi..

even i got the same error message after clearing the tf..

Jan 2013-2-12

@Azzi: This means, that there is a TF function for dfilt objects. The same happens, if you add a function in a subfolder like @uint32\strcmp.m. Then calling strcmp(uint32('a')) calls this user-defined function instead of Matlab's builtin STRCMP.

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