FFTW
====

FFTW is highly optimized, but downgrades if run on an older processor. It
should be built compiled on merlin, since it needs SSE2, AVX2, and Infiniband
(libfabric).

This module requires PMODULE_VERSION > 1.0.0 to compile.

The module is currently organized around several use flags:

- *sp* single precision vs *dp* double precision
- *merlin6* vs *merlin*. These come from the upstream dependency on openmpi,
  which needs to be compiled differently for RHEL6 (merlin) and RHEL7
  (merlin6).


