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MathGroup Archive 2002

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RE: how to extract parameter values

  • To: mathgroup at smc.vnet.net
  • Subject: [mg37324] RE: [mg37310] how to extract parameter values
  • From: "DrBob" <drbob at bigfoot.com>
  • Date: Wed, 23 Oct 2002 02:57:09 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Try this:

plot = ParametricPlot[{Cos[5t], Sin[3t]}, {
      t, 0, 2ð}, AspectRatio -> Automatic];
lines = Cases[plot, _Line, Infinity]

To learn more about what's going on, look at

Head[plot]
plot[[1]]
plot[[2]]

Also note that you can operate on a graph my manipulating its first
argument.  For instance, to do a coordinate transformation:

A = {{1, 2}, {-3, 1}};
Show[Graphics[plot[[1]] /. {x_, y_} -> A.{x, y}, plot[[2]]]]

Bobby

-----Original Message-----
From: Jan Mangaldan [mailto:jajem at yahoo.com] 
To: mathgroup at smc.vnet.net
Subject: [mg37324] [mg37310] how to extract parameter values


I'd like to know how I can extract the parameter
values used by ParametricPlot in plotting a curve,
e.g. if ParametricPlot used points corresponding to
parameter values 2, 4, 6, etc... I need a way to get
the list {2, 4, 6, ...}.

One solution I know is this:

list={};
ParametricPlot[(AppendTo[list,t]; {f[t]
g[t]}),{t,tmin,tmax}];

The problem with this is that I get an error that
ParametricPlot cannot compile the function, and that
the plotting time is considerably slowed down.
especially if I have a high PlotPoints setting.

Any ideas?

                                   Jan Mangaldan (~_~)

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