CURVE /VARIABLE

      [GREG1\]CURVE /VARIABLE V [Array_V]

    Selects the the interpolation variable V, which may be
      - X                 To plot a function Y=F(X) (Default)
      - Y                 To plot a function X=F(Y)
      - Z  [Array_V]      To plot a curve with an  explicit  parametrization
        using  the  Z array, or the array Array_V if this second argument is
        present.
      - POLYGONAL_LENGTH  To plot a curve using the polygonal length of  the
        curve as parametrization. It is fast and of general use.
      - CURVILINEAR_LENGTH Refined and slow version of  the  parametrization
        in POLYGONAL_LENGTH.
      - NUMBERING          The parameter is the numbering of points.  It  is
        only   appropriate   if   the   numbering   reflects   a  reasonable
        parametrization of the curve.