
Galactic Algorithms (2010) - Anon84
https://rjlipton.wordpress.com/2010/10/23/galactic-algorithms/
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BeetleB
In lay terms, an example of a galactic algorithm is one which has better big O
complexity than algorithms currently in use, but where the crossover point of
better performance than the status quo requires an incredibly large N - so
large that we can't conceive any practical problem where this algorithm will
perform better.

For example, you may need an N larger than the number of stars in the
universe. Hence the term "galactic". I've seen another one that requires an N
larger than the number of atoms in the universe.

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kevinventullo
A somewhat famous, more recent example:
[https://news.ycombinator.com/item?id=19474280](https://news.ycombinator.com/item?id=19474280)

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voidmain
The Fastest and Shortest Algorithm for All Well-Defined Problems [1]

An algorithm M is described that solves any well-defined problem p as quickly
as the fastest algorithm computing a solution to p, save for a factor of 5 and
low-order additive terms.

(The constants in the "low order" terms are... large. Basically this is a
delightful reductio of asymptotic analysis)

[1] [https://arxiv.org/abs/cs/0206022](https://arxiv.org/abs/cs/0206022)

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tectonic
From the article: "A galactic algorithm is an algorithm that is wonderful in
its asymptotic behavior, but is never used to actual compute anything."

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phomer
Yes. Theoretically the algorithm is tractable, but the exponent is so large
that it wouldn't be practical to run it in a real environment.

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amelius
According to the article, the algorithm does not need to have a polynomial
bound to be classified as "galactic".

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phomer
It is mentioned a couple times explicitly, but I think most of the readers for
this blog would know that the border line for tractable is polynomial growth.
Still, it is an interesting observation, worth investigating.

