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Given a random instance $I_m = I_m(n,k)$ of $k$-SAT with $n$ variables and $m$ clauses, what's the probability $I_m$ is satisfiable?

It's believed that there's a threshold above which satisfiability becomes less likely as $m/n$ increases. The reverse is true as $m/n$ decreases.

Is there an empirical formula for $3$-SAT and other $k$'s that describe the rate at which satisfiability becomes more/less likely as you move away from the threshold?

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    $\begingroup$ I don't think there is a formula. See Moshe Vardi's talk about phase transition. $\endgroup$ – Kaveh Feb 11 '14 at 19:04
  • $\begingroup$ Tyr to use surround your latex code with $ to make it more readable. I am unsure how you wanted it to display $\endgroup$ – Martin Vatshelle Feb 11 '14 at 20:21
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    $\begingroup$ what is an "empirical formula"? $\endgroup$ – Sasho Nikolov Feb 11 '14 at 20:39
  • $\begingroup$ @Kaveh - thanks for the video. Very enlightening. $\endgroup$ – dcs Feb 11 '14 at 22:05
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    $\begingroup$ See the answers at cstheory.stackexchange.com/q/14953/109 for several key references. This actually seems borderline a duplicate of that question? $\endgroup$ – András Salamon Feb 12 '14 at 11:30
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see eg sec 4.7.4 p103 of this thesis where a finite-size scaling formula based on a power law is applied and coefficients fit with experimental data.

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  • $\begingroup$ fyi/addendum nobody called this out but full disclosure, that section seems to be on bounded SAT which is closely related to k-SAT but not the same. however the empirical formulas seem to be almost the same for k-SAT & they seem to have originated in statistical physics spin-glass transition point formulas. another ref critical behavior in the computational cost of satisfiability checking 1996 Selman/Kirkpatrick see eg p276. [wish there were newer refs/study on this subj, havent seen them] $\endgroup$ – vzn Feb 18 '14 at 3:46

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