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(gnuplot.info)parametric

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 The `set parametric` command changes the meaning of `plot` (Note: plot )
 ((`splot` (Note: splot )) from normal functions to parametric
 functions.  The command `set noparametric` restores the plotting style to
 normal, single-valued expression plotting.

 Syntax:
       set parametric
       set noparametric
       show parametric

 For 2-d plotting, a parametric function is determined by a pair of parametric
 functions operating on a parameter.  An example of a 2-d parametric function
 would be `plot sin(t),cos(t)`, which draws a circle (if the aspect ratio is
 set correctly---see `set size` (Note: size )).   `gnuplot`
 (Note: gnuplot ) will display an error message if both functions are not
 provided for a parametric `plot`.

 For 3-d plotting, the surface is described as x=f(u,v), y=g(u,v), z=h(u,v).
 Therefore a triplet of functions is required.  An example of a 3-d parametric
 function would be `cos(u)*cos(v),cos(u)*sin(v),sin(u)`, which draws a sphere.
 `gnuplot` will display an error message if all three functions are not
 provided for a parametric `splot`.

 The total set of possible plots is a superset of the simple f(x) style plots,
 since the two functions can describe the x and y values to be computed
 separately.  In fact, plots of the type t,f(t) are equivalent to those
 produced with f(x) because the x values are computed using the identity
 function.  Similarly, 3-d plots of the type u,v,f(u,v) are equivalent to
 f(x,y).

 Note that the order the parametric functions are specified is xfunction,
 yfunction (and zfunction) and that each operates over the common parametric
 domain.

 Also, the `set parametric` function implies a new range of values.  Whereas
 the normal f(x) and f(x,y) style plotting assume an xrange and yrange (and
 zrange), the parametric mode additionally specifies a trange, urange, and
 vrange.  These ranges may be set directly with `set trange` (Note: trange ),
  `set urange` (Note: urange ), and `set vrange` (Note: vrange ), or by
 specifying the range on the plot or splot commands.  Currently the default
 range for these parametric variables is [-5:5].  Setting the ranges to
 something more meaningful is expected.