jsteinhardt comments on Post Request Thread - Less Wrong

20 Post author: Qiaochu_Yuan 11 April 2013 01:28AM

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Comment author: jsteinhardt 14 April 2013 04:30:59PM 4 points [-]

Hm...the set of NP-complete problems where there is a polynomial-time approximation scheme is not that large, and the approximation schemes can sometimes be pretty bad (i.e. getting answers within 1% takes time n^100). Besides, Bayesian inference is at least #P-complete, possibly P-space complete, and a 1% error in the prior blows up to arbitrarily large error in the posterior, so approximation algorithms won't do anyways.

Comment author: evand 15 April 2013 04:18:18PM 0 points [-]

I'm curious to learn more.

My general impression (having studied computer science, and complexity theory in passing, but being far from an expert) is that bounded-error approximations are not as well studied as precise solutions. I also get the impression that most of the bounded-error complexity results are results for specific approximation algorithms, not proofs about the limits of such algorithms. Are impossibility results for bounded-error approximations common?

In other words,

the set of NP-complete problems where there is a polynomial-time approximation scheme is not that large

Do you mean the set where such approximations are known, or the set where they are not known to be impossible?