Forward FFT for non-periodic-X case
We transpose X<->Y so that the non-periodic direction becomes the
"Y" direction in the transposed space, then use the same FFT approach as 010
Nodes of different colours represent the following:
Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.
Where possible, edges connecting nodes are
given different colours to make them easier to distinguish in
large graphs.