

Using A Slime-Mold To Calculate Minimum Spanning Trees - rfreytag
https://www.nytimes.com/2012/05/13/opinion/sunday/the-wisdom-of-slime.html?_r=1

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ColinWright
Related:

<http://news.ycombinator.com/item?id=1071093>

<http://news.ycombinator.com/item?id=1071533>

<http://news.ycombinator.com/item?id=1071568>

<http://news.ycombinator.com/item?id=1072876>

<http://news.ycombinator.com/item?id=3406446>

<http://news.ycombinator.com/item?id=3477746>

<http://news.ycombinator.com/item?id=3728933>

<http://news.ycombinator.com/item?id=3757527>

<http://news.ycombinator.com/item?id=3853748>

Very few have comments, but the stories are varied.

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scott_s
I'm calling out this one because it has video, which I think people who read
the NY Times article would like to see: [http://phys.org/news/2012-03-slime-
mold-mimics-canadian-high...](http://phys.org/news/2012-03-slime-mold-mimics-
canadian-highway.html)

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rfreytag
Soap films approximate minimum spanning trees. See:
[http://csunplugged.org/sites/default/files/activity_pdfs_ful...](http://csunplugged.org/sites/default/files/activity_pdfs_full/unplugged-15-steiner_trees_0.pdf)
(see page 7 [aka, page 157]).

Actually, these films approximate Steiner Trees; which is harder (NP-
complete): <https://en.wikipedia.org/wiki/Steiner_tree_problem>

EDIT: replaced 'find' and 'solve' with 'approximate.' EDIT: added '(NP-
complete)'.

~~~
jerf
Only for sufficiently small definitions of "solve":
<http://arxiv.org/pdf/quant-ph/0502072v2>

Definitions which turn out to be very small indeed.

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tocomment
Another one of those articles where they really should include a picture of
the network the mold came up with. A picture really would say 1000's of words
in this case; they spend the whole article describing what the mold did :-(

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royhodgman
Arxiv has a paper by Andrew Adamatzky (one of the authors of the nytimes
article) called "Are motorways rational from slime mould’s point of view?",
from 13 Mar 2012, which has pictures:

<http://arxiv.org/pdf/1203.2851.pdf>

Take a look at page 4.

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mjn
If we view slime molds as a sort of computing machine, which responds
differently to different inputs, an intriguing angle is to use it for
generative art, the way people use other computing formalisms like context-
free grammars (<http://www.contextfreeart.org>), cellular automata, and other
things.

The tricky thing is that slime mold tends to either die or gunk everything up
if you aren't careful, but there are some artists "collaborating" with it in
producing paintings, which makes for interesting outcomes sometimes because
the mold seems to carry pigments around, and responds differently to different
pigments and preparations of surfaces: <http://slimoco.ning.com/>

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davidw
So what kind of algorithm does the slime mold use?

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Dn_Ab
My naive guess is hill climbing based on chemical gradients. I have a strong
hunch that large networks settle at local optimums.

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ghoul2
I'd say more likely its equivalent to particle filters. Mold probably shoots
spores all around the petri dish, and the spores that have better access to
nutrients grow more, thus putting out larger proportion of spores in the next
generation. A few generations later, all organisms that are either directly
next to the nutrients, or next to another organism which has good access to
nutrients survive.

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danpalmer
My Tutor at university (Computer Science) is one of the leading experts on
using Slime-Molds in computation. He makes robots controlled by them. Very
interesting stuff I think, although biological computing isn't normally my
area of interest.

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lucian1900
Very interesting. I don't think slime-molds are fast enough to build a useful
NP-oracle, though.

~~~
pmiller2
MST is polynomial, so you can't use it as an NP oracle, anyway.

~~~
hythloday
And the fact that the slime molds didn't create the same layout every time
implies they don't provide an optimum answer.

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ganley
Not necessarily true. There could be multiple, equal-valued optima.

~~~
pmiller2
Exactly. Consider the case of all equal weights. In that case, every spanning
tree is a MST. For the extreme cases (labeled complete graph, and a tree) of
order n, those numbers are $n^{n-2}$ and 1, respectively, so the answer can be
far from unique.

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majmun
Next step : connect slime-mold to virtual reality , and expose API for it.

