Finding index of a maximum value in an FFT

In a simple model I graph my FFT and I can clearly see the index of the peak value, but I can't get it "mathematically" so to speak. I tried peak finder but couldn't get it to work. Attaching my results.

Answer 1

[KSSV]

doc max

[Marek Andrzej]

Is that a function or a method? I'm sorry, I didn't understand your answer.

[KSSV]

It is a function......Read the documentation of max

[Marek Andrzej]

I used max in the past for same task in matlab, but simulink counterpart doesn't seem to be helpful. Both peak finder and maximum blocks gave me the same index, which is hardly correlate-able to 50Hz wave. buffer outputs 4096 points of data and Pad adds 4096 zeros.