FFT of sine function

I am trying to plot power of sine function. When I do FFT of sine wave I got two peaks for a single sin function. I don't know understand it. Why do I get two frequency spikes from a simple sin function via FFT? How can I get only one peak for a single sin function?

Answer 1

[sloppydisk]

You'll get both positive and negative frequencies, see

doc fft

for an example of a single-sided spectrum, i.e. only positive frequencies.