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P versus NP and other resource-bounded computation.

16 votes
Accepted

Simple question about decision problems

You are right: formally P includes only decision problems. But many decision problems have corresponding optimization problems: find the size of the largest matching in a graph, find the length of the …
Aaron Roth's user avatar
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13 votes

Are there NP-complete problems with polynomial expected time solutions?

There is a polynomial time algorithm for finding Hamiltonian cycles on random graphs, that succeeds asymptotically with the same probability that a Hamiltonian cycle exists. Of course, this problem is …
Aaron Roth's user avatar
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13 votes
Accepted

Is minimax problem NP-Hard when the inner problem is NP-Hard ?

The answer to your question is "no", although for natural problems that you might be thinking about, it may be a good heuristic that if the inner problem is NP hard, the whole problem is probably hard …
Aaron Roth's user avatar
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7 votes

Can testing show the absence of bugs?

To continue along the lines of Deigo's answer, standard sample complexity bounds from learning theory tell you that if you are satisfied with finding a program which is "approximately correct", you do …
Aaron Roth's user avatar
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6 votes
Accepted

Hardness of approximation assuming the existence of one-way functions

The problem of learning in the PAC model is really just a problem of combinatorial optimization: with a large enough sample size, finding a function $f \in C$ which has low prediction error is equival …
Aaron Roth's user avatar
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12 votes

How hard is Mafia?

Here's a reference that you will want to look at: http://www.jstor.org/stable/10.2307/25442651 Mafia: A theoretical study of players and coalitions in a partial information environment Braverman, M. …
Aaron Roth's user avatar
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8 votes
Accepted

Hardness of MAX-CUT on sparse graphs

There cannot be significantly better algorithms for graphs with $O(n\log n)$ edges than there are for general graphs. This is because the Benczur-Karger cut sparsifier can take an arbitrary graph, and …
Aaron Roth's user avatar
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5 votes
Accepted

How do you compute the fixed point of a best-response function efficiently?

A fixed point of a best response function is a Nash equilibrium -- the fact that you do not have the payoff matrix cannot make the problem easier (since if you know the payoff matrix, you also know th …
Aaron Roth's user avatar
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36 votes
Accepted

Is integer factorization an NP-complete problem?

No, its not known to be NP-complete, and it would be very surprising if it were. This is because its decision version is known to be in $\text{NP} \cap \text{co-NP}$. (Decision version: Does $n$ have …
Aaron Roth's user avatar
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3 votes

Why do theoreticians in CS use multiple-letter variables?

I'm not sure I agree with your premise. I think in most papers, you will find short variable names: some of my personal favorites are $n$, $m$, $i$, $k$, $\epsilon$, and $\alpha$, each quite concise! …
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27 votes
Accepted

Parameterized complexity from P to NP-hard and back again

One field with lots of non-monotonicity of problem complexity is property testing. Let $\mathcal{G}_n$ be the set of all $n$-vertex graphs, and call $P \subseteq \mathcal{G}_n$ a graph property. A gen …
Aaron Roth's user avatar
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34 votes
5 answers
3k views

Evidence that PPAD is hard?

There is often-quoted philosophical justification for believing that P != NP even without proof. Other complexity classes have evidence that they are distinct, because if not, there would be "surprisi …
Aaron Roth's user avatar
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13 votes

The importance of Integrality Gap

When you are coming up with an approximation algorithm for some NP-hard maximization problem, there are several values that you might care about: There is OPT, the optimal value of your problem, which …
Aaron Roth's user avatar
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8 votes

Why economists should care about computational complexity

Main stream game theorists are, I think, becoming much more open to contemporary work in the computer science community, so it may be less necessary to "make the case'' for algorithmic game theory tha …
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