AssertionError for number of processors equals array dimension

[benlandrum]

This probably doesn't happen often in practice, but using 3 processors for the below code triggers an assertion error in pencil.py (link to line). 2 processors causes no problems.

import numpy as np
from mpi4py import MPI
from mpi4py_fft import PFFT, newDistArray

# This works on 2 processors, but not 3.
shape = np.array((2, 2, 3), dtype=int)

fft = PFFT(MPI.COMM_WORLD, shape=shape, dtype=float)

u = newDistArray(fft, forward_output=False)
u[...] = np.random.random(u.shape).astype(u.dtype)

u_hat = newDistArray(fft, forward_output=True)

# AssertionError
fft.forward(u, u_hat)

If this case is not supported, I would like to request that this raise an exception with descriptive text rather than just hit an assert.