diff options
Diffstat (limited to 'numpy/fft/fftpack.py')
| -rw-r--r-- | numpy/fft/fftpack.py | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/numpy/fft/fftpack.py b/numpy/fft/fftpack.py index c70e336ea..472d3e06c 100644 --- a/numpy/fft/fftpack.py +++ b/numpy/fft/fftpack.py @@ -296,12 +296,14 @@ def rfft(a, n=None, axis=-1): compute the negative frequency terms, and the length of the transformed axis of the output is therefore ``n//2+1``. - When ``A = rfft(a)``, ``A[0]`` contains the zero-frequency term, which - must be purely real due to the Hermite symmetry. - - If `n` is even, ``A[-1]`` contains the term for frequencies ``n/2`` and - ``-n/2``, and must also be purely real. If `n` is odd, ``A[-1]`` - contains the term for frequency ``A[(n-1)/2]``, and is complex in the + When ``A = rfft(a)`` and fs is the sampling frequency, ``A[0]`` contains + the zero-frequency term 0*fs, which must be purely real due to the Hermite + symmetry. + + If `n` is even, ``A[-1]`` contains the term representing both positive + and negative Nyquist frequency (+fs/2 and -fs/2), and must also be purely + real. If `n` is odd, there is no term at fs/2; ``A[-1]`` contains + the largest positive frequency (fs/2*(n-1)/n), and is complex in the general case. If the input `a` contains an imaginary part, it is silently discarded. |