building waform from formula node

Dear Sir,

I am trying to build a waveform from output of a formula node.

I have fitted a 10th order polynomial on  frequency response of my system and in the code i have inverted the system and found out amplitude
(AMP) and phase (PHA) at different harmonics of fundamental frequency f.

Now i construct the signals (f0) with 10000 point by adding up the harmonic content at each harmonic frequency.

I want to generate a continuous signal.

Could you suggest what is wrong with the code