# How the transfer function block calculates the output?

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Joseph Stalin on 5 Dec 2012
Hi, Actually I am trying to understand the maths behind the MATLAB transfer function block,for reverse engineering some control system blocks.
I have done the following operation to check my understanding. 1.I took a test transfer function (tf)ex: 2.5/(s+2.5) 2.given a ramp input, the tf response I have plotted. 3.for the same transfer function I took a inverse laplase transform and it resulted in 2.5*e^(-2.5t).Again for a ramp input, I have plotted this response.
I compared both the results.I felt both must be matching.But it didn't. anybody help me out in understanding why the results are different?

Babak on 5 Dec 2012
Edited: Babak on 5 Dec 2012
2.5*e^(-2.5t)
is the Laplace inverse of
2.5/(s+2.5)
not
(2.5/s+2.5).
The Laplace transform of
(2.5/s+2.5)
includes an impulse function.
Babak on 6 Dec 2012
Now, with your fixed question, please let us know how you are doing the ramp? I looked up ramp in MATLAB control toolbox functions but cannot find any function doing this...Are you doing it in Simulink? or you wrote your own ramp input function?