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Inverse Laplace Transform for a complex transfer function

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Darren Tran
Darren Tran on 10 Dec 2019
Answered: Darren Tran on 30 Dec 2019 at 23:02
For my signals project I was able to represent a system using a transfer function consisting of 50 zeros and 60 poles. However, when I tried to get the time domain function of this laplace domain impulse response using ilaplace() with the numerators and denominators as inputs, the code has been running for hours with no end.
I understand that due to the complexity of the transfer function matlab may not be able to find an exact answer. Is there a way to estimate or possible improve the identification of this time domain equation? Thank you


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David Goodmanson
David Goodmanson on 11 Dec 2019
Hi Darren,
There are not positions of poles and zeros here, just two polynomials with coefficients. Those coefficients all have values like -6.226e14 (+/- 1.801e23), meaning that they are of no use at all. You might want to consider how realistic it is to have a transfer function with 50 poles and 60 zeros. If you did know, accurately, the positions of all those poles and zeros then it's certainly possible to find the answer numericaly in short order, but there could well be big problems with numerical accuracy in such a calculation.
Walter Roberson
Walter Roberson on 11 Dec 2019
-6.226e14 (+/- 1.801e23) is pretty much a nonsense number, with inprecision 1 billion times larger than the number itself.
Are these numbers coming from the output of cftool (Curve Fitting Toolbox) ?
Shashwat Bajpai
Shashwat Bajpai on 26 Dec 2019
I would be in a better state to help you if the coefficients mentioned are in a MATLAB executable format.

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Answers (1)

Darren Tran
Darren Tran on 30 Dec 2019 at 23:02
Hello I have found the solution. The 50 poles 60 zeros method was wrong and I ended up using 2 zeroes and three poles. I then did an inverse laplace and found the original function. Than you everyone for you help.


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