How to convert symbolic expressions to transfer functions
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Qian Feng
on 31 Oct 2016
Commented: Walter Roberson
on 7 Aug 2023
I am encountering the problem of converting a symbolic expression to become a transfer function. Specifically, the linear system I am dealing with contains a non-constant distributed delay term which requires performing an integration to obtain the corresponding transfer function. However, it seems that the integration operator int cannot be applied with tf variables directly.
On the other hand, if there is a way to convert symbolic expressions to transfer functions, then this problem can be easily handled in symbolic setting first.
Thanks a lot
3 Comments
Star Strider
on 1 Nov 2016
I suggested a similar approach yesterday. It’s apparently not a polynomial.
Accepted Answer
Walter Roberson
on 2 Nov 2016
12 Comments
Paul
on 27 Feb 2021
Cool code. Siight mod to also handle the case when symExp is a constant.
syms s
symExp(s) = 5;
ExpFun = matlabFunction(symExp);
ExpFun = str2func(regexprep(func2str(ExpFun), '\.([/^\\*])', '$1'));
TF = tf(ExpFun(tf('s')));
TF
TF =
5
Static gain.
More Answers (2)
HyunSang Park
on 28 May 2018
If you're just trying to find the peak value of the bode magnitude plot, might I suggest avoid using tf altogether? the peak value is when d(G(jw))/dw = 0. You can easily find the derivative with syms, and the plug in the w to the original tf.
0 Comments
Murugan venkatesan
on 7 Aug 2023
In order to analyze the bifurcation, the input impedance expression how to plot the bode graph..
1 Comment
Walter Roberson
on 7 Aug 2023
I do not understand how people can use your answer to convert symbolic expressions to transfer functions? Could you show how your solution could be used for the example symExp = (s+2)/(s^2+5*s+9); ?
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