I tried the method described in a previous answer (https://math.stackexchange.com/a/718856/451691) to compute the transfer function of a system I am studying, where:
In(t) = a(t); Out(t) = b(t)
I did as suggested below using a Scilab code:
Let A(f) and B(f) be the FFT's from a(t) respectively b(t).
Then you're supposed to take the inverse FFT from B(f)/A(f). It will result > in an array of real values that identifies the transfer function with respect to time.
But, when I multiply this array (that I call h) by the array of input values, the result is massively different from the output values I computed resolving the system's differential equations.
In symbols:
h = IFFT(B(f)/A(f))
In(t)*h ~= Out(t)
What is wrong with this method?