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