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MathGroup Archive 2007

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Re: Strange RegionPlot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81569] Re: Strange RegionPlot
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Fri, 28 Sep 2007 02:06:44 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fddfh1$a67$1@smc.vnet.net>

Bruce Colletti wrote:

> Re 6.0.1 under Windows XP.
> 
> The region returned by:
> 
> RegionPlot[x + y < 4 && x - y > 3, {x, -20, 25}, {y, -20, 10}]
> 
> should be triangular.  Yet the apex is a short line segment and not a vertex.  
> 
> What creates this segment, and what must one do to get the vertex?  Thankx.

Hi Bruce,

A good guess is that the adaptive sampling scheme is set too low for 
this graphic. A value of 4 or 5 for the option *MaxRecursion* should 
yield the correct result.

GraphicsColumn[
  RegionPlot[x + y < 4 && x - y > 3, {x, -20, 25}, {y, -20, 10},
     ImageSize -> 400, MaxRecursion -> #,
     PlotLabel -> StringJoin["MaxRecursion -> ", ToString@#]] & /@
   Range[0, 10]]

(Or see http://homepages.nyu.edu/~jmg336/mathematica/StrangeRegionPlot.pdf)

Regards,
-- 
Jean-Marc


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