Fwd: Extracting points from a contour plot

• To: mathgroup at smc.vnet.net
• Subject: [mg90544] Fwd: Extracting points from a contour plot
• From: "Jean-Marc Gulliet" <jeanmarc.gulliet at gmail.com>
• Date: Sat, 12 Jul 2008 05:33:27 -0400 (EDT)
• References: <5.2.1.1.2.20080711154413.01680098@postoffice8.mail.cornell.edu>

```I am just forwarding Greg's message since it was momentarily unable to
post to MathGroup.
- Jean-Marc

On Fri, Jul 11, 2008 at 9:45 PM, Greg Ezra <gse1 at cornell.edu> wrote:
>
>>(Note that we can also use *Reduce* to get a set of analytic solutions.)
>>
>>   g = ContourPlot[Cos[x] + Cos[y] == 0, {x, 0, 2 Pi}, {y, 0, 2 Pi}]
>>
>>   FullForm[g]
>>
>>   pts = First@Cases[g, x_GraphicsComplex :> First[x]]
>>
>>   MapThread[Chop[Cos[#1] + Cos[#2]] == 0 &, Transpose@pts]
>>
>>   Reduce[Cos[x] + Cos[y] == 0 && 0 <= x <= 2 Pi && 0 <= y <= 2 Pi, {x,
>>   y}]
>>
>>Regards,
>>-- Jean-Marc
>>
>
>
> Hello:
>
>
> Apologies for email but I am unable to post at the moment.
>
> A ListPlot of pts obtained as above looks fine.
>
> On the other hand, using
>
>  g = ContourPlot[Cos[x] + Cos[y], {x, 0, 2 Pi}, {y, 0, 2 Pi},Contours->{0}]
>
> yields many points that lie completely off the correct contour!
>
> I had successfully used a similar procedure to evaluate functions along
> contours in V5; it no longer works in V6, however.
>
> Do you have any idea what might have changed in ContourPlot in V6?
>
> Thanks,
>
> Greg Ezra

```

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