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MathGroup Archive 2002

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Re: non integer exponents in ContourPlot[]?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35228] Re: non integer exponents in ContourPlot[]?
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Wed, 3 Jul 2002 05:13:31 -0400 (EDT)
  • References: <afrgq3$lt1$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Rob,
The function is not evaluating to a *real* number at some pointgs (this
should have been made explicit in the message)
There are several ways out, one is to change the function to Re[...].

Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565


"1.156" <rob at piovere.com> wrote in message news:afrgq3$lt1$1 at smc.vnet.net...
> Mathematica wizards all:
>
> The following code runs fine, note the (apparent) floating point form of
the exponents.
>
> a=-5.75;b=2;d=1.1;
>
> ContourPlot[a*((x^2.0 + y^2.0)^0.5 + b*y^2.0), {x, -d, d}, {y, -d, d},
ContourShading -> False,
>    Contours -> {-6, -3, -1}, PlotPoints -> 30];
>
> But, if I make any of the 2.0 exponents say, 2.1, I get big error messages
like
>
> 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.
>
> However, it works fine if I change the 0.5 exponent to say, 0.55.
>
> Can anyone give me a hint of what's going on here? I'd sure like to be
able to play with these exponents to fit some data.
>
> Thanks, Rob
>
>




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