ifft after signal processing

Hello,

I've followed tutorial (https://it.mathworks.com/help/matlab/ref/fft.html) for obtaining fft. I've multyplied "P1" (name as per tutorial) by the transfer function of the SDOF equivalent object and now I want to obtain the amplified signal in the time domain. The point is that, applying the ifft, I obtain again a complex number, instead of a real one only. Which is my mistake? Should I work on imaginary numbers without following the tutorial?

Many thanks and regards

Davide

[Dana]

Can you post your actual code, rather than just describing it? It's very difficult to figure out what you're trying to do and what might have gone wrong without seeing the code.