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MathGroup Archive 2005

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Re: locating points in mathematica plots

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57637] Re: locating points in mathematica plots
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at 9online.fr>
  • Date: Thu, 2 Jun 2005 05:18:02 -0400 (EDT)
  • Organization: New York University
  • References: <d7k39c$oiq$1@smc.vnet.net>
  • Reply-to: jmg336 at nyu.edu
  • Sender: owner-wri-mathgroup at wolfram.com

utish_r at hotmail.com wrote:
> how to locate points (coordinate), say maxima and minima values, in a
> 3d plot in mathematica?
> 
Not whether this is what you are looking for.

Assuming that you use some experimental data where only "z" is provided 
and ListPlot3D, we generate a surfacegraphics to start with:

In[100]:=
data = Table[Sin[x*y] + Random[Real, {-0.15, 0.15}],
     {x, 0, (3*Pi)/2, Pi/15}, {y, 0, (3*Pi)/2, Pi/15}];

In[101]:=
p2 = ListPlot3D[data];

The internal structure of the expression is of the form

In[102]:=
Shallow[FullForm[p2], {6, 2}]

SurfaceGraphics[List[List[-0.0531853132797791`, 0.07470139085368`,
Skeleton[21]], List[-0.04314815332538362`, -0.004767344336139311`,
       Skeleton[21]], Skeleton[21]],
     List[Rule[
       PlotRange, Automatic], RuleDelayed[DisplayFunction, 
$DisplayFunction], Skeleton[37]]]

So we can find, say, the maximum using

In[103]:=
Max[p2[[1]]]

Out[103]=
1.12698

and the corresponding coordinates by

In[104]:=
Position[p2[[1]], Max[p2[[1]]]]

Out[104]=
{{23,9}}

Hope this helps,
/J.M.


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