Compute the onedimensional fft for real input.
Return the n point discrete Fourier transform of the real valued array a. n defaults to the length of a. n is the length of the input, not the output.
Parameters:  a : array
n : int
axis : int


Notes
The returned array will be the nonnegative frequency terms of the Hermitesymmetric, complex transform of the real array. So for an 8point transform, the frequencies in the result are [ 0, 1, 2, 3, 4]. The first term will be real, as will the last if n is even. The negative frequency terms are not needed because they are the complex conjugates of the positive frequency terms. (This is what I mean when I say Hermitesymmetric.)
This is most efficient for n a power of two.