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MathGroup Archive 2004

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Re: How to modify Convex Hull program to give output as Cartesian Coordinates?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg48766] Re: [mg48760] How to modify Convex Hull program to give output as Cartesian Coordinates?
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Wed, 16 Jun 2004 04:54:05 -0400 (EDT)
  • References: <200406150650.CAA27195@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 15 Jun 2004, at 15:50, Gilmar Rodr?guez Pierluissi wrote:

> Greetings Mathematica Group!:
>
> I use the following example, to formulate my question:
>
> In[1]: data2D = {{4.4, 14}, {6.7, 15.25}, {6.9, 12.8}, {2.1, 11.1},
>                 {9.5, 14.9},{13.2, 11.9}, {10.3, 12.3}, {6.8, 9.5},
>                 {3.3, 7.7}, {0.6, 5.1},{5.3, 2.4},{8.45, 4.7},
>                 {11.5, 9.6},{13.8, 7.3}, {12.9, 3.1}, {11, 1.1}};
>
> In[2]: << DiscreteMath`ComputationalGeometry`
>
> In[3]: convexhull = ConvexHull[data2D]
>
> Out[3]: {14,6,5,2,1,4,10,11,16,15}
>
> My question is:
>
> Is there any way to modify the ConvexHull program to give the
> Cartesian coordinates of the points corresponding to the values
> 14,6,5,2,1,4,10,11,16,15; instead of Out[3] above?
>
> Thank you!
>
>

Yes.

convexhull = data2D[[ConvexHull[data2D]]]


{{13.8, 7.3}, {13.2, 11.9}, {9.5, 14.9}, {6.7, 15.25},
   {4.4, 14}, {2.1, 11.1}, {0.6, 5.1}, {5.3, 2.4},
   {11, 1.1}, {12.9, 3.1}}

Andrzej Kozlowski
Chiba, Japan
http://www.mimuw.edu.pl/~akoz/


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