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For every integer $t$, is there a problem whose solutions can be verified in $O(n^{s})$ time but cannot be found in $O(n^{st})$ time?

By verifying, I mean that given a candidate solution $y$, we can judge whether $y$ is correct or not in time $O(n^s)$.

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  • $\begingroup$ I'm not familliar with $\omega$ notation, do you mean $\Omega$ notation? $\endgroup$ May 7, 2013 at 4:42
  • $\begingroup$ I edited your question to reflect your comment on the A.Schulz answer, I don't know if this edit is correct or not, but IMO Schulz answer was correct before this edit. $\endgroup$
    – user742
    May 7, 2013 at 10:03
  • $\begingroup$ @jmite $\omega$ notation is standard Landau notation. It is to $\Omega$ as $o$ is to $O$. $\endgroup$
    – Pål GD
    May 9, 2013 at 10:55
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    $\begingroup$ "Can be computed in $\omega(n^5)$ time" does not mean the same thing as "cannot be computed in $O(n^5)$ time". It is possible to buy a pencil for more than a million dollars, but that doesn't imply that I can't buy a pencil for less than a million dollars. $\endgroup$
    – JeffE
    May 9, 2013 at 14:36
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    $\begingroup$ What's the quantifier on $s$? Do you mean "For all integers $s$ and $t$, is there a problem..." or do you mean "For every integer $t$, is there an integer $s$ and a problem..." or do you mean "Is there an integer $s$ such that for every integer $t$ there is a problem..."? $\endgroup$
    – JeffE
    May 9, 2013 at 14:39

2 Answers 2

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For $k = \left\lceil \dfrac{r}{2} \right\rceil$, it is conjectured (and proven in some simpler models of computation by JeffE) that $r$-SUM problem has lower bounds $\Omega(n^k)$, the solution for which can be verified in $O(n)$ time.

Pick an $r$ such that $k \gt t$, implying $\omega(n^t)$ bounds.

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  • $\begingroup$ Where is it proven? $\endgroup$
    – Shayan
    May 8, 2013 at 18:53
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    $\begingroup$ @Shayan: Did you check out the link? (click on conjectured in the answer) $\endgroup$
    – Aryabhata
    May 8, 2013 at 22:13
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    $\begingroup$ You can find my $r$-SUM lower bound paper here and a more readable followup paper here. $\endgroup$
    – JeffE
    May 10, 2013 at 14:53
  • $\begingroup$ But the answer is proved for "simpler models of computation" not generally. $\endgroup$
    – Shayan
    May 10, 2013 at 16:39
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If I understood you correctly, it is okay if $s=t=1$. In this case take sorting in some comparison based model. You can verify a correct solution with $O(n)$ comparisons. On the other hand you need $\Omega(n \log n)\subsetneq \omega(n)$ comparisons to sort.

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    $\begingroup$ But I want to solve it for every integer t. Not a single sample. $\endgroup$
    – Shayan
    May 7, 2013 at 9:55

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