build_periodic_shift_values Subroutine

  subroutine build_periodic_shift_values(plan, shift_axis1, shift_axis2, nshift)
    type(fmm_plan_type), intent(in) :: plan
    real(dp), intent(out) :: shift_axis1(:), shift_axis2(:)
    integer(i32), intent(out) :: nshift
    integer(i32) :: s, img

    nshift = 1_i32
    shift_axis1(1) = 0.0d0
    shift_axis2(1) = 0.0d0
    if (.not. plan%options%use_periodic2) return

    nshift = 2_i32*plan%options%periodic_image_layers + 1_i32
    if (size(shift_axis1) < nshift .or. size(shift_axis2) < nshift) then
      error stop 'periodic shift buffer is too small.'
    end if
    do s = 1_i32, nshift
      img = s - plan%options%periodic_image_layers - 1_i32
      shift_axis1(s) = real(img, dp)*plan%options%periodic_len(1)
      shift_axis2(s) = real(img, dp)*plan%options%periodic_len(2)
    end do
  end subroutine build_periodic_shift_values