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MathGroup Archive 2002

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Re: non integer exponents in ContourPlot[]?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35247] Re: [mg35209] non integer exponents in ContourPlot[]?
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Wed, 3 Jul 2002 05:16:06 -0400 (EDT)
  • References: <200207020612.CAA22327@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Ok, just beware of complex numbers. It is very hard to get them into a plot.
You see, for example,

In[1]:=
x^2 .0/. x -> -1.1
Out[1]=
1.21

a real number. However,

In[2]:=
x^2.1 /. x -> -1.1
Out[2]=
1.161798 + 0.377491*I

a complex number. The function you obtain when you change the exponents from
2.0 to 2.1 is impossible to plot. (Incidentally, in Mathematica a number
such as 2.0 or 2.1 is not called "floating point", but just "real").

Tomas Garza
Mexico City
----- Original Message -----
From: "1.156" <rob at piovere.com>
To: mathgroup at smc.vnet.net
Subject: [mg35247] [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
>
>



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