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MathGroup Archive 2010

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Random points in triangle

  • To: mathgroup at smc.vnet.net
  • Subject: [mg111573] Random points in triangle
  • From: "S. B. Gray" <stevebg at ROADRUNNER.COM>
  • Date: Fri, 6 Aug 2010 06:55:22 -0400 (EDT)
  • Reply-to: stevebg at ROADRUNNER.COM

I was looking for a simple way to place random points inside a triangle 
with uniform distribution. Here's a good way:

newtri := Module[{x},
   ptri = RandomReal[{-5, +5}, {3, 2}];
   tredg = Subsets[ptri, {2}];
   ]
newpts[nump_] := Module[{wts},
   inpoints = {};
        Do [ wts = RandomReal[GammaDistribution[1, 2], 3];
           wts = wts/Total[wts];
           newin = Total[ptri*wts];
          inpoints = Append[inpoints, newin], {nump}];
   ]
shotri := Module[{x},
   Graphics[{Blue, Line[tredg], Red, Point[inpoints]}, ImageSize -> 500]
   ]

The same idea works for points in a tetrahedron; they will be uniformly 
distributed if you use args such as GammaDistribution[.6,.1].

Steve Gray


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