Setup the FFTs for calculating the parallel spectrum
subroutine init_par_filter
use theta_grid, only: ntgrid
use gs2_transforms, only: init_zf
use kt_grids, only: naky, ntheta0
use mp, only: proc0
implicit none
if (naky * ntheta0 == 0) then
if (proc0) print *,"WARNING: kt_grids used in init_par_filter before initialised?"
end if
call init_zf (ntgrid, ntheta0*naky)
end subroutine init_par_filter