updated fft doc
@@ -72,4 +72,6 @@ CuPy functions do not follow the behavior, they will return ``numpy.complex64``
Internally, ``cupy.fft`` always generates a *cuFFT plan* (see the `cuFFT documentation`_ for detail) corresponding to the desired transform. When possible, an n-dimensional plan will be used, as opposed to applying separate 1D plans for each axis to be transformed. Using n-dimensional planning can provide better performance for multidimensional transforms, but requires more GPU memory than separable 1D planning. The user can disable n-dimensional planning by setting ``cupy.fft.config.enable_nd_planning = False``. This ability to adjust the planning type is a deviation from the NumPy API, which does not use precomputed FFT plans.
+Moreover, the automatic plan generation can be surpressed by using an existing plan returned by ``cupyx.scipy.fftpack.get_fft_plan`` as a context manager. This is again a deviation from NumPy.
+
.. _cuFFT documentation: https://docs.nvidia.com/cuda/cufft/index.html
