# calculate input of a system having output and transfer function

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hossein on 3 Oct 2018
Commented: Raghunandan V on 5 Oct 2018
Dear Friends Hi, I want to identify a complex system. I have used several transfer functions in my system. in one part of my code I have to calculate the input of a system while I have the output and the transfer function consider y=TF*x, I have TF and y and want to estimate x. if I use the TF^-1 or inv(TF) the error of "Cannot simulate the time response of models with more zeros than poles." will occur. So dear friend what is your suggestions and/or solutions?
hossein on 5 Oct 2018
why u need the transfer function? for example, u can consider: GW = ( 0.2245 s + 9.002)/(s^2 + 161.4 s + 6448)
consider any kind of stable transfer function (number of poles> number of zeros). when u inverse the transfer the function number of poles will be less than the number of zeros which means the inversed transfer function is unstable. so I can not use the x=TF^-1*y. therefore I am seeking an alternative,

Raghunandan V on 5 Oct 2018
https://dsp.stackexchange.com/questions/16671/output-of-a-system-given-its-transfer-function-and-input-beginner
Does this solve your question? And you cannot directly enter a transfer function with more zeros than poles and hence use the original transfer function and then use inverse or division block for your purpose I am sure this will work
Raghunandan V on 5 Oct 2018
could you share the .m file. i can take a look at it