How do I calculate an area in Mathematica?

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Discussion Overview

The discussion revolves around calculating the area of a specific region in 3D space defined by inequalities, particularly the intersection of a hollow sphere and a solid toroid-like surface using Mathematica. Participants explore methods for estimating this area, including numerical approaches and considerations for point distribution.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant inquires about calculating the area of a region defined by inequalities in Mathematica, specifically for the intersection of a hollow sphere and a solid toroid-like surface.
  • Another participant suggests a Monte Carlo method, proposing to randomly generate points on the surface of the sphere and check if they lie within the toroid-like surface to estimate the area.
  • A later reply acknowledges the suggestion, noting that the area could be approximated by multiplying the sphere's area by the fraction of points that fall inside the toroid.
  • Participants discuss the importance of ensuring uniform distribution of points when randomly generating them on the sphere's surface to avoid inaccuracies in the area estimation.
  • One participant expresses gratitude for the advice regarding point distribution, recognizing the potential issue of denser point selection near the poles if latitude and longitude are chosen randomly.

Areas of Agreement / Disagreement

Participants generally agree on the proposed Monte Carlo method for estimating the area, but there is no consensus on the best approach for ensuring uniform point distribution, highlighting a potential area of contention.

Contextual Notes

Participants have not fully resolved the mathematical steps involved in ensuring uniform point distribution or the implications of using different methods for point generation.

IridescentRain
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Hi!

Say I have a region described by any number of inequalities. This region is a surface in 3D space. How can I ask Mathematica to calculate the region's area?

If it helps, my particular region is the intersection of a hollow sphere and a solid (i.e. filled-out) toroid-like surface. I'm using Mathematica 9, but I think I can find a Mathematica 8 .dmg file and my old license key if necessary.

Thanks!
 
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Since no one has offered any idea and perhaps you might still see this...

Suppose you randomly generate a point on the surface of your sphere.
Then check to see whether that point is inside the toroid like surface.
Repeat that perhaps 10^6 times. See what fraction of those are inside.
Does that fraction tell you something interesting or useful?

Note: If you did not have a hollow sphere to start with then this might
be more complicated. You might think about why that might be.
 
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Thanks for the suggestion. With a million points, that would make a very good approximation. (Obviously, the area of my region would be the sphere's area times the fraction of points inside the torus.)

Cheers!
 
Wonderful. Just be very careful with that random generation so that the points are uniformly distributed across the sphere. Doing something like randomly choosing a latitude and then randomly choosing a longitude would not make the points uniformly distributed and would lead to an inaccurate estimate of the area.
 
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Ah, thanks for the advice. It's perfectly reasonable now that you've mentioned it, yet I would have probably gone and done just that --randomly select a latitude and a longitude-- without realising that the point distribution would then be denser near the poles. I'll be more careful than that with my random-point selection.

Cheers!
 

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