       Re: non integer exponents in ContourPlot[]?

• To: mathgroup at smc.vnet.net
• Subject: [mg35234] Re: [mg35209] non integer exponents in ContourPlot[]?
• From: BobHanlon at aol.com
• Date: Wed, 3 Jul 2002 05:14:04 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```In a message dated 7/2/02 4:05:59 AM, rob at piovere.com writes:

>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},
>   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.

You are generating complex numbers.

a=-5.75;b=2;d=1.1;

Table[a*((x^2.0+y^2.1)^0.5+b*y^2.0),
{x,-1,1,.5}, {y,-1,1,.5}]//
Chop//TableForm

ContourPlot[
a*((x^2.0+y^2.1)^0.5+b*y^2.0),
{x,-d,d},{y,0,d},
Contours->{-6,-3,-1},
PlotPoints->30];

Table[a*((x^2.1+y^2.0)^0.5+b*y^2.0),
{x,-1,1,.5}, {y,-1,1,.5}]//
Chop//TableForm

ContourPlot[
a*((x^2.1+y^2.0)^0.5+b*y^2.0),
{x,0,d},{y,-d,d},