The FFT of a real vector gives a symmetric complex FFT. Because of the symmetry we only have to store (and process) one half of the result. If we add this feature then users can decide if they want to:
Convert the real vector into a complex vector, Fourier transform the vector and obtain both halfs of the spectrum
Perform the FFT on the real vector directly and obtain only half of the spectrum
The FFT of a real vector gives a symmetric complex FFT. Because of the symmetry we only have to store (and process) one half of the result. If we add this feature then users can decide if they want to: