anchor.diff:      end select
     end function
     
  -  !----------------------------------------------------------
  -  ! find the normal vector of this hexahedron's k_th surface
  -  !----------------------------------------------------------
  +  !-------------------------------------------------------
  +  ! find the normal vector of this element's k_th surface
  +  !-------------------------------------------------------
     function findEleSurfNorm(this,k)
       class(typeEle),intent(in)::this
       integer,intent(in)::k
  
positive.code:     end select
    end function
    
    !---------------------------------------------------
    ! find the center of this hexahedron's k_th surface
    !---------------------------------------------------
    ! Note: actually we are finding the average position of the vertices
    function findEleSurfPC(this,k)
      class(typeEle),intent(in)::this
  
negative.code:     end select
    end function
    
    !----------------------------------------------
    ! find the area of this element's k_th surface
    !----------------------------------------------
    function findEleSurfArea(this,k)
      class(typeEle),intent(in)::this
      integer,intent(in)::k
  