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Statistical distributions of areas of Voronoi cells

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POSTED BY: Vitaliy Kaurov
10 Replies

You may be interested in this paper, which takes a semi-empirical approach to come up with a closed-form approximate formula:

At the time when it was written, Mathematica did not have VoronoiMesh, but one could "trick" it to quickly compute a Voronoi tessellation by using ListDensityPlot with InterpolationOrder -> 0 and extracting the polygons.

POSTED BY: Szabolcs Horvát
Posted 7 years ago

Very Nice. I am aware that the distribution of Lightning strike intensity from a Thunderstorm also closely follows a Gamma Distribution. Could this be due to cells of charge inside the cloud which organise like a Voronoi topology? Does a Gamma distribution also arise from a 3 D distribution of volumes of a Vornoi tesellation?

POSTED BY: BJ Miller
Posted 7 years ago
POSTED BY: Erik Mahieu

Great, @Erik, thanks for exploring further and sharing!

POSTED BY: Vitaliy Kaurov

Dear All,

that is indeed interesting. I also believe that the exact distribution is unknown but it can be approximated by a GammaDistribution, see:

https://arxiv.org/pdf/1207.0608.pdf

https://arxiv.org/pdf/1612.02375.pdf

https://www.sciencedirect.com/science/article/pii/002608008990030X

http://www.scipress.org/journals/forma/pdf/1804/18040221.pdf

http://www.eurecom.fr/~arvanita/PVT.pdf

Interestingly, if you run the code in @Vitaliy Kaurov's cod for 50000 points you obtain:

dis = FindDistribution[areas]
(*GammaDistribution[3.2718, 0.0000197063]*)

I managed to get it done for 500000 points. I think that the edge effects should be getting smaller; as the area increases faster than the circumference.

So I obtain:

dis = FindDistribution[areas, 5]

(*
{MixtureDistribution[{0.658342, 0.341658}, {MaxwellDistribution[2.92588*10^-6], GammaDistribution[7.1867, 1.37091*10^-6]}], 

ExtremeValueDistribution[4.80446*10^-6, 2.73831*10^-6], 

GammaDistribution[2.94963, 2.17794*10^-6], 

BetaDistribution[2.94962, 459143.], 

MixtureDistribution[{0.687855, 0.312145}, {MaxwellDistribution[2.82857*10^-6], 
   LogNormalDistribution[-11.5031, 0.28619]}]}*)

This happens when we plot all of them:

Plot[Evaluate[PDF[#, x] & /@ dis], {x, 0, 0.00003}, PlotRange -> All, LabelStyle -> Directive[Bold, 16]]

enter image description here

If you compare that with the histogram:

Show[Histogram[areas, 200, "PDF"], Plot[Evaluate[PDF[#, x] & /@ dis], {x, 0, 0.00003}, PlotRange -> All,LabelStyle -> Directive[Bold, 16]]]

enter image description here

I would say that the second (ExtremeValueDistribution) fits best:

enter image description here

but it does not get the small areas quite right.

Regarding the boundary effects, one might also (similar to what Sander suggests) use the torus as the geometry:

disfun[x_, y_] := Sqrt[Min[Abs[x[[1]] - y[[1]]], 1 - Abs[x[[1]] - y[[1]]]]^2 + Min[Abs[x[[2]] - y[[2]]], 1 - Abs[x[[2]] - y[[2]]]]^2]

M = 50; nf = Nearest[Rule @@@ Transpose[{RandomReal[1, {M, 2}], Range[M]}], DistanceFunction -> disfun]

DensityPlot[First[nf[{x, y}]], {x, 0, 1}, {y, 0, 1}, PlotPoints -> 100, ColorFunction -> "TemperatureMap"]

enter image description here

Cheers,

Marco

POSTED BY: Marco Thiel
POSTED BY: Vitaliy Kaurov

I don't find it all that surprising that the result is a Gamma distribution. The 1-d case is well known as it is the distribution of interarrival times of a Poisson process and is exponentially distributed. The exponential distribution is a special case of the Gamma so maybe you're onto something.

POSTED BY: Carlo Barbieri
POSTED BY: Sander Huisman

Thanks! Awesome idea about edge-effects! Did you estimate any analytical models beyond Gamma or it was just pure empirical thing?

POSTED BY: Vitaliy Kaurov

I looked at different things: how many sides, angles, area, perimeter, and many conditionally averaged quantities. But area of the PDF as well. But no analytical shape is known for it. I believe that there is something known for perimeter.

POSTED BY: Sander Huisman
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