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MathGroup Archive 2000

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Re: ContourPlot doesn't work properly?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23848] Re: [mg23829] ContourPlot doesn't work properly?
  • From: BobHanlon at aol.com
  • Date: Mon, 12 Jun 2000 01:17:38 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 6/10/2000 3:31:49 AM, higra at gugu.usal.es writes:

>Let's take a common function like y=Exp[x]
>If I try to make a picture of this function in an implicit way with 
>ContourPlot in the form
>ContourPlot[Log[y]-x,{x,-10,10},{y,-10,10}, 
>PlotPoints->30,Contours->{0},ContourShading->False]
>
>with the option PlotPoints->30 in order to have a more precise picture
>I obtain an error message:
>
>    ContourGraphics::ctpnt:
>
>    The contour is attempting to traverse a cell in which some of the
>    points have not evaluated to numbers, and it will be dropped.
>
>and no picture.
>
>But if I let the option PlotPoints his default value the message is the
>same, but now the picture is drawn.
>
>Could anyone explain what happens?
>

With the default value it is more tolerant of errors and draws whatever it 
can. 

You need to avoid specifying a region where Log[y] is complex. Use

ContourPlot[Log[y] - x, {x, -10, 10}, {y, 0.000001, 10}, 
PlotPoints -> 30, Contours -> {0}, ContourShading -> False];


Bob

BobHanlon at aol.com


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