op_obj_d1dx1 Function

    impure function op_obj_d1dx1(this,in) result(out)
      !> Computes the derivative in the x1-direction.
      ! Note: If input is face-centered (on x1), result is
      ! cell-centered (on x1m). If input is cell-centered (on x1m),
      ! result is face-centered (on x1).
      class(op_obj),        intent(in) :: this                                 !! Differential operators utility
      type(eulerian_obj_r), intent(in) :: in                                   !! Field to differentiate
      type(eulerian_obj_r)             :: out                                  !! Result
      ! Work variables
      integer :: i,j,k
      integer :: slo, shi

      call out%Initialize('d1dx1',this%block,this%parallel,in%staggering)

      associate (lo => this%block%lo,  hi => this%block%hi)
        select case (in%staggering)
        case (0,2,3)
          ! From xm to x
            do k=lo(3),hi(3)
              do j=lo(2),hi(2)
                do i=lo(1),hi(1)
                  slo = i - this%st
                  shi = i + this%st - 1

                  out%cell(i,j,k)=dot_product(this%c_d1dx1m(:,i),in%cell(slo:shi,j,k))
                end do
              end do
            end do
        case (1)
          ! From x to xm
            do k=lo(3),hi(3)
              do j=lo(2),hi(2)
                do i=lo(1),hi(1)
                  slo = i - this%st + 1
                  shi = i + this%st

                  out%cell(i,j,k)=dot_product(this%c_d1dx1 (:,i),in%cell(slo:shi,j,k))
                end do
              end do
            end do
        end select
      end associate

      return
    end function op_obj_d1dx1