[SciPy-User] rfft

[garyr]

If I generate a sine wave of a particular frequency in an array of type 
float32 or float64 and compute the transform using the function fft (in 
scipy/fftpack/basic.py) I find the signal in the correct bin. If I use the 
function rfft, which is described as returning the Fourier transform of a 
real sequence,  I find the signal in the bin corresponding to twice the 
actual frequency. I thought rfft would be the proper function to use for 
real (non-complex) data. What is the correct usage of rfft?