op_obj_conv33 Function

    impure function op_obj_conv33(this,in1,in2) result(out)
      !> Computes d(U3 U1)/dx1.
      class(op_obj),        intent(in) :: this                                 !! Differential operators utility
      type(eulerian_obj_r), intent(in) :: in1                                  !! Convecting velocity: Ui
      type(eulerian_obj_r), intent(in) :: in2                                  !! Velocity Uj
      type(eulerian_obj_r)             :: out                                  !! Result
      ! Work variables
      type(eulerian_obj_r) :: in1c                                             !! Interpolated Ui from face to cell center
      integer :: i,j,k,n

      call in1c%Initialize('in1c',     this%block,this%parallel,3             )
      call out%Initialize('ddx3(U3U1)',this%block,this%parallel,in2%staggering)
      out = 0.0_wp

      in1c = this%intrp3(in1)
      call in1c%UpdateGhostCells

      associate (lo => this%block%lo,  hi => this%block%hi)
       do k=lo(3),hi(3)
         do j=lo(2),hi(2)
           do i=lo(1),hi(1)
             do n = -this%st, this%st-1
               out%cell(i,j,k) = out%cell(i,j,k) + this%c_d1dx3m(n,k)*in1c%cell(i,j,k+n)* &
                                                 0.5_wp*(in2%cell(i,j,k+2*n+1)+in2%cell(i,j,k))
             end do
           end do
         end do
       end do
      end associate

      return
    end function op_obj_conv33