type_variable_shift Subroutine

    subroutine type_variable_shift(self, reverse)
        class(type_variable), intent(inout) :: self
        logical, intent(in), optional :: reverse
        logical :: do_reverse

        do_reverse = .false.
        if (present(reverse)) then
            do_reverse = reverse
        end if

        if (do_reverse) then
            if (self%rank > 0) then
                self%pre(:) = self%old(:, 1)
                ! 履歴を左にシフト (old(:,1) <--- old(:,2), ...)
                if (self%rank > 1) then
                    self%old(:, 1:self%rank - 1) = self%old(:, 2:self%rank)
                end if
                ! 空いた最後の履歴をクリア
                self%old(:, self%rank) = 0.0d0
            end if

        else
            self%pre(:) = self%new(:)
            if (self%rank > 0) then
                ! 履歴を右にシフト (old(:,2) <--- old(:,1), ...)
                if (self%rank > 1) then
                    self%old(:, 2:self%rank) = self%old(:, 1:self%rank - 1)
                end if
                self%old(:, 1) = self%pre(:)
            end if
        end if

    end subroutine type_variable_shift