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MathGroup Archive 2002

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RE: non integer exponents in ContourPlot[]?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35226] RE: [mg35209] non integer exponents in ContourPlot[]?
  • From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
  • Date: Wed, 3 Jul 2002 05:13:26 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

> -----Original Message-----
> From: 1.156 [mailto:rob at piovere.com]
To: mathgroup at smc.vnet.net
> Sent: Tuesday, July 02, 2002 8:12 AM
> To: mathgroup at smc.vnet.net
> Subject: [mg35226] [mg35209] non integer exponents in ContourPlot[]?
> 
> 
> 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
> 
> 

Rob,

perhaps you might like to try

expon = 3.;  (* or 2.1, or ... *) 

ContourPlot[
    a*(Abs[x^expon + y^expon]^0.5 + b*Abs[y]^expon), {x, -d, d}, {y, -d, d},
     ContourShading -> False, Contours -> {-6, -3, -1}, PlotPoints -> 100];


--
Hartmut


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