init_3d Subroutine

  subroutine init_3d (nny_in, nnx_in, how_many_in)
    use fft_work, only: init_crfftw, init_rcfftw, delete_fft, FFT_TO_SPECTRAL_SPACE, FFT_TO_REAL_SPACE
    implicit none
    integer, intent(in) :: nny_in, nnx_in, how_many_in
    integer, save :: nnx, nny, how_many

    if (initialized_3d) then
       if (nnx /= nnx_in .or. nny /= nny_in) then
          call delete_fft(xf3d_cr)
          call delete_fft(xf3d_rc)
       elseif ( how_many /= how_many_in) then
          call delete_fft(xf3d_cr)
          call delete_fft(xf3d_rc)
       else
          return
       end if
    end if
    initialized_3d = .true.
    nny = nny_in
    nnx = nnx_in
    how_many = how_many_in

#if FFT == _FFTW3_
    call init_crfftw (xf3d_cr, FFT_TO_REAL_SPACE, nny, nnx, how_many)
    call init_rcfftw (xf3d_rc, FFT_TO_SPECTRAL_SPACE, nny, nnx, how_many)
#endif

  end subroutine init_3d