anchor.diff:              area(i,j) = sum_area
            enddo
         enddo
  -
  -      write(6,'(A,E24.16)') 'area = ', area(1,1)
   
         end
   
  
positive.code:             tlen = sqrt(taup(1)**2 + taup(2)**2 + taup(3)**2)
  
              DO m = 1,3
                 xtangents(i,j,m) = taup(m)/tlen
              ENDDO
              edge_lengths(i,j,1) = tlen
           ENDDO
  
negative.code: 
  c           # nv has unit length
              do m = 1,3
  c               ytangents(i,j,m) = taup(m)/tlen
                 ytangents(i,j,m) = taup(m)
              enddo
              edge_lengths(i,j,2) = tlen
           enddo
  