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<H2><A NAME="SECTION0402450000000000000000"></A>
<A NAME="commands_set_parametric"></A><A NAME="commands_unset_parametric"></A><A NAME="commands_show_parametric"></A><A NAME="set_parametric"></A><A NAME="unset_parametric"></A><A NAME="show_parametric"></A><A NAME="parametric"></A><A NAME="5706"></A>
<A NAME="noparametric"></A><A NAME="5708"></A>
<BR>
Parametric
</H2>
The <B>set parametric</B> command changes the meaning of <B>plot</B> (<B>splot</B>) from
normal functions to parametric functions. The command <B>unset parametric</B>
restores the plotting style to normal, single-valued expression plotting.
<P>
Syntax:
<BR>
<PRE>
set parametric
unset parametric
show parametric
</PRE>
<BR>
<P>
For 2D plotting, a parametric function is determined by a pair of parametric
functions operating on a parameter. An example of a 2D parametric function
would be <B>plot sin(t),cos(t)</B>, which draws a circle (if the aspect ratio is
set correctly -- see <B>set size (p. <A HREF="node260.html#set_size"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]" SRC="crossref.png"></A>)<A NAME="5717"></A></B>). <B>gnuplot</B> will display an error message if
both functions are not provided for a parametric <B>plot</B>.
<P>
For 3D 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 3D parametric
function would be <B>cos(u)*cos(v),cos(u)*sin(v),sin(u)</B>, which draws a sphere.
<B>gnuplot</B> will display an error message if all three functions are not
provided for a parametric <B>splot</B>.
<P>
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, 3D plots of the type u,v,f(u,v) are equivalent to
f(x,y).
<P>
Note that the order the parametric functions are specified is xfunction,
yfunction (and zfunction) and that each operates over the common parametric
domain.
<P>
Also, the <B>set parametric</B> 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 <B>set trange</B>, <B>set urange</B>,
and <B>set vrange</B>, or by specifying the range on the <B>plot</B> or <B>splot</B>
commands. Currently the default range for these parametric variables is
[-5:5]. Setting the ranges to something more meaningful is expected.
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2010-08-17
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