anchor.diff:  !   Plot using 2d coordinate transform
       call plenv(-1.0_plflt, 1.0_plflt, -1.0_plflt, 1.0_plflt, 0, 0)
       call plcol0(2)
  -    call plcont(z, 1, nptsx, 1, nptsy, clevel, xg2, yg2)
  +    call plcont(z(1:nptsx,1:nptsy), 1, nptsx, 1, nptsy, clevel, xg2(1:nptsx,1:nptsy), yg2(1:nptsx,1:nptsy))
       call plstyl(1, 1500, 1500)
       call plcol0(3)
  -    call plcont(w, 1, nptsx, 1, nptsy, clevel, xg2, yg2)
  +    call plcont(w(1:nptsx,1:nptsy), 1, nptsx, 1, nptsy, clevel, xg2(1:nptsx,1:nptsy), yg2(1:nptsx,1:nptsy))
       call plstyl(0, 1500, 1500)
       call plcol0(1)
       call pllab('X Coordinate', 'Y Coordinate', 'Streamlines of flow')
  
positive.code:     call pl_setcontlabelparam(0.006_plflt, 0.3_plflt, 0.1_plflt, 1)
      call plenv(-1.0_plflt, 1.0_plflt, -1.0_plflt, 1.0_plflt, 0, 0)
      call plcol0(2)
      call plcont(z, 1, nptsx, 1, nptsy, clevel, tr)
      call plstyl(1, 1500, 1500)
      call plcol0(3)
      call plcont(w, 1, nptsx, 1, nptsy, clevel, tr)
      call plstyl(0, 1500, 1500)
      call plcol0(1)
      call pllab('X Coordinate', 'Y Coordinate', 'Streamlines of flow')
  
negative.code: !   Plot using 1d coordinate transform
      call plenv(-1.0_plflt, 1.0_plflt, -1.0_plflt, 1.0_plflt, 0, 0)
      call plcol0(2)
      call plcont(z(1:nptsx,1:nptsy), 1, nptsx, 1, nptsy, clevel, xg1(1:nptsx), yg1(1:nptsy))
      call plstyl(1, 1500, 1500)
      call plcol0(3)
      call plcont(w(1:nptsx,1:nptsy), 1, nptsx, 1, nptsy, clevel, xg1(1:nptsx), yg1(1:nptsy))
      call plstyl(0, 1500, 1500)
      call plcol0(1)
      call pllab('X Coordinate', 'Y Coordinate', 'Streamlines of flow')
  