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# Questions tagged [relativization]

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### Which is harder, an NP-complete problem or the Raz-Tal oracle problem?

This is a (hopefully) sharper version of a question that I asked previously. Which of these algorithms is believed to have a longer asymptotic runtime? The optimal algorithm guaranteed to solve some ...
14 views

### Do relativized relations between complexity classes tell us anything about the nonrelativized relation?

The existence of relativized relations between complexity classes seems to often be treated as "circumstantial" evidence about the "true" or "real-world" (i.e. nonrelativized) relation between the ...
35 views

### Finding a language that is $NP^L$-complete

I'm trying to prove a theorem and as a lemma I would like to identify an $NP^L$-complete language. I was thinking something like a machine that can decide $SAT$ equipped with an oracle for $L$ can ...
43 views

### The power of relativised proofs

I've been trying to understand why, for instance, even though there are oracles $A$ for which $P^A \neq NP^A$, we still don't know if $P=NP$. As I understand it, it's because it's easy to construct ...
20 views

### Any barrier result for this kind of (non-relativising) technique?

We think that non-deterministic machines are more powerful than deterministic machines, by giving an oracle access to $P\subseteq L\subseteq NP$, it seems reasonable to expect there's some $L$ that is ...
42 views

### Cook-Levin theorem and relativization

An answer in the post How can I show that the Cook-Levin theorem does not relativize? gives a proof that there exists an oracle B and a language L in the class $NP^B$ such that there is no oracle ...
78 views

43 views

### Complete problems and relativization barriers for nonuniform complexity classes

Do nonuniform complexity classes like NP/poly have complete problems? Are there relativization barriers for separations of nonuniform complexity classes? One way to interpret the second question is ...
1k views

### How can I show that the Cook-Levin theorem does not relativize?

The following is an exercise which I am stuck at ( source: Sanjeev Arora and Boaz Barak; its not homework ) : Show that there is an oracle $A$ and a language $L \in NP^A$ such that $L$ is not ...
156 views

### Is $BQP$ in $P^{NP}$?

I read in the introduction of this paper http://www.scottaaronson.com/papers/uncompute.pdf that there is a problem $B$ such that $BQP^B \not\subset P^{NP^B}$, and that $B$ is in $BPP$. But, using ...
180 views

### Relativization of NP-completeness [duplicate]

This is actually exercise 3.7 from "Computational Complexity: A Modern Approach". I need to prove that the NP-Completeness of 3-sat does not relativize, i.e. I need to show that that exists some ...
532 views

### The meaning of relativization

I don't understand the notion of relativization. I expose with an example. Consider a class $A$ that contains $P$, e.g. $NP$. Why $P^A$ is not necessarily equal to $A$? I can naively think that if one ...
304 views

### Is it axiomatic that the Time Hierarchy Theorem holds true in all relativized worlds?

I learned from this post that ${\sf DTIME}^{\text{EXP}}(n^k) \neq \text{EXP}$ for a fixed $k$ for otherwise the Time Hierarchy Theorem would fail in that relativized world. However, is it possible to ...
126 views

### Why does the principle of locality of computation not relativize?

Although I have trouble understanding oracle TMs, I appreciate that non-relativizing techniques will be needed to resolve P vs. NP (as well as most other open problems in TCS). However, one of the ...
1k views

### Why are non-relativizing proofs preferred to relativizing ones?

I apologize, but even after these two other posts: here and here I'm still having trouble understanding oracle TMs and relativization. This question comes at the issue from a different angle: Why ...
566 views

### Confusion about the Time Hierarchy Theorem and relativization

I know that $\mathsf{P}^A = \mathsf{EXP}$ for any $\mathsf{EXPTIME}$-complete language $A$. Is it true that $\mathsf{DTIME}^A(n^k) = \mathsf{EXP}$ for any fixed $k$ and any $\mathsf{EXPTIME}$-...
1k views

### Intuition behind Relativization

I take course on Computational Complexity. My problem is I don't understand Relativization method. I tried to find a bit of intuition in many textbooks, unfortunately, so far with no success. I will ...
How to prove that $\mathsf{NP}^A \neq \mathsf{coNP}^A$ ? I am just looking for a such oracle TM $M$ and a recursive language $L(M) = L$ for which this holds. I know the proof where you show that ...
When I was explaining the Baker-Gill-Solovay proof that there exists an oracle with which we can have, $\mathsf{P} = \mathsf{NP}$, and an oracle with which we can have $\mathsf{P} \neq \mathsf{NP}$ to ...