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In the Karma Bites You in the Ass Department: - F*cking with Clusters

About In the Karma Bites You in the Ass Department:

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For your amusement, a partial transcript of yesterday's research meeting:

Advisor: The brain regions in this database work on a nearest neighbor rule. ...
A: In my head: Nearest neighbor. Easy. But wait! Boundary conditions...
Advisor: To get the boundaries, though, you have to think of them as expanding soap bubbles.
A: No. No please. Anything... anything but...
Advisor: Have you ever heard of Voronoi diagrams?
A: NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

As a sidenote, do any of you happen to know of a half-decent implementation of Voronoi diagrams in 3-space?
Current Mood: resigned
Current Music: Winnings
take a penny
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From:mbrubeck
Date:September 23rd, 2005 09:08 pm (UTC)
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HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!!!!!!!
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From:profgreg
Date:September 25th, 2005 07:59 pm (UTC)
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What he said
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From:avani
Date:September 26th, 2005 12:32 am (UTC)
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Luckily, I already hate you both ;-)
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From:willworker
Date:September 23rd, 2005 09:58 pm (UTC)
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Huh?

My local CS expert also isn't sure what you're talking about. Could you explain? Brain regions? Nearest neighbor rule? Voronoi diagrams?

Steve
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From:avani
Date:September 23rd, 2005 10:12 pm (UTC)
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So, say that you have 2 points. Point 1 represents group A, the other represents group B. Nearest neighbor is the rule that for every new point, if its closer to the first point, its in group A, and if its closer to the second, its in group B. You can draw the line separating group A and group B between points 1 and 2. Expanding that to many points, that gives you a basic idea of what a Voronoi diagram is.

http://mathworld.wolfram.com/VoronoiDiagram.html

The brain part is that I'm working with the Talairach database, which is a sparse and, from what I've heard, vaguely incorrect database of points mapped to about 152 brain regions. I'm trying to come up with a good visualization for it.
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From:csn
Date:September 24th, 2005 09:36 am (UTC)
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Very interesting, I would like to learn more.
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From:tortoise
Date:September 23rd, 2005 10:52 pm (UTC)
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Wow.
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From:amoken
Date:September 24th, 2005 01:15 am (UTC)
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Only 2-space, sorry. :(

Out of curiosity, why do you hate them so?
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From:avani
Date:September 24th, 2005 01:37 am (UTC)

Wow, this node still exists!

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http://www3.hmc.edu/~rgarfinkel/funwiki/index.cgi?DoYourCompGeoAvani

We had to do a 2-space implementation as a final project.

(and no, I never finished ;-) )
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From:amoken
Date:September 24th, 2005 01:44 am (UTC)

Re: Wow, this node still exists!

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Ah. I have to do Voronoi-related stuff for work.
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From:istgut
Date:September 24th, 2005 07:38 am (UTC)
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i read a paper that used 3d delaunay. i am not sure if it is still the dual of the the 3d voronoi.

unfortunately, having moved out of my lab and put all of my shit in a BigAssPile in the middle of my bedroom, i do not currently know the location of said paper.

depending on what you need your output to be... do you just need nearest neighbors? because if you just need nearest neighbors, then a 2D implementation should be able to be quickly changed into a 3D implementation just by chaning the distance metric from 2D to 3D.
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From:istgut
Date:September 24th, 2005 07:38 am (UTC)
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and i've got all kinds of 2D voroni laying around :)
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From:istgut
Date:September 24th, 2005 07:39 am (UTC)
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n log n, even :)
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From:avani
Date:September 26th, 2005 12:31 am (UTC)
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Huh.. that might just work. I need nearest neighbor, and some way to at least approximately draw region boundaries for a set of 3-d regions.
(take a penny)
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