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MathGroup Archive 2000

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RegionPlot ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23489] RegionPlot ?
  • From: "Seth Chandler" <SChandler at uh.edu>
  • Date: Fri, 12 May 2000 22:54:28 -0400 (EDT)
  • Organization: University of Houston
  • Sender: owner-wri-mathgroup at wolfram.com

Right now, the function Experimental`CylindricalAlgebraicDecomposition
yields a list of inequalities. For inequalities with two variables, I would
like to be able to plot the region showing where that inequality is
satisfied.

By way of simple example:

In[69]:=
ecad = Experimental`CylindricalAlgebraicDecomposition[{x + y <= 3, x - y
> -4,
       x >= 0, y >= 1}, {x, y}]

Out[69]=
0 <= x < 2 && 1 <= y <= 3 - x || x == 2 && y == 1

What I would like to do is something like:

RegionPlot[ecad,{x,-3,5},{y,-3,7}].

The output would be Polygon primitives, Line primitives,  and a Point
primitive

Any thoughts on how to implement this?

Obviously, one could approximate the matter by creating a table of x,y
values and plotting at {x,y} a primitive of some shape and size for each
table element satisfying the set of inequalities.  I was hoping someone
might come up with something more elegant, however. (Maybe ContourPlot used
in some way?)





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