pm.ParticleMesh has to have ndim > 1?

[nickhand]

Is it true that the mesh in the new ParticleMesh has to have at least 2 dimensions? It seems so from the test cases.

I am getting an error from pmesh trying to make 1D ParticleMesh objects

pm = ParticleMesh(BoxSize=1.0, Nmesh=[16], dtype='f4')

yields ValueError: ProcMesh (1) shall have less dimentions than Mesh (1)

[rainwoodman]

It is not that trivial. It appears that pfft dies with divide by zero error if we plan a 1d transform on a single rank.

[rainwoodman]

I may have found a way to work it out with pfft together with mpip/pfft#30