
3D Theory - Collision Detection - octopus
http://www.euclideanspace.com/threed/animation/collisiondetect/index.htm
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rflrob
> For example if we have 'n' objects then the first object could collide with
> n-1 objects (since we don't check if an object has collided with itself) the
> second object could collide with (n-2) additional objects not counting the
> possible collisions we have already counted. If we keep going like this we
> get the number of possible collisions is: (n-1) * (n-2) * (n-3) ... 1 This
> is equivalent to n! / 2! * (n-2)!

Seems to me like it should be more like the handshake problem, which comes out
to n * (n-1)/2. n^2 is still bad, but not nearly as bad as n!.

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IvoDankolov
Actually, n! / (2! * (n-2)!) comes out exactly at n * (n-1)/2. It's just one
form of the general formula for combinations.

However, multiplying the possible situations is, of course, wrong. A case of a
wrong explanation of the final result I'd imagine (permutations instead of
combinations),

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newobj
Hrmm. For some reason whenever graphics/game programming related articles get
posted on HN, the quality seems to be ridiculously low. For example, no
discussion of discrete vs. continuous, temporal coherence, sweep and prune,
separating axis, etc. I think even if you assume this article was written in
1998 it still strikes me as a bit behind the times. The fact that this article
has 15 points at the moment is disturbing...

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Entlin
Why don't you post a better article?

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newobj
Because I haven't been involved in game development professionally since 2002.
Even though my knowledge is now 9 years out of date, I know that this article
is low quality.

