• Corpus ID: 6267695

A Lasserre-based $(1+\varepsilon)$-approximation for $Pm \mid p_j=1, \textrm{prec} \mid C_{\max}$

@article{Levey2015AL,
  title={A Lasserre-based \$(1+\varepsilon)\$-approximation for \$Pm \mid p\_j=1, \textrm\{prec\} \mid C\_\{\max\}\$},
  author={Elaine Levey and Thomas Rothvoss},
  journal={ArXiv},
  year={2015},
  volume={abs/1509.07808}
}

• Elaine Levey, T. Rothvoss
• Published 25 September 2015
• Computer Science
• ArXiv

In a classical problem in scheduling, one has $n$ unit size jobs with a precedence order and the goal is to find a schedule of those jobs on $m$ identical machines as to minimize the makespan. It is one of the remaining four open problems from the book of Garey & Johnson whether or not this problem is $\mathbf{NP}$-hard for $m=3$.
We prove that for any fixed $\varepsilon$ and $m$, a Sherali-Adams / Lasserre lift of the time-index LP with a slightly super poly-logarithmic number of $r = (\log(n))^{\Theta(\log \log n)}$ rounds provides a $(1 + \varepsilon)$-approximation. This implies an algorithm that yields a $(1+\varepsilon)$-approximation in time $n^{O(r)}$. The previously best approximation algorithms guarantee a $2 - \frac{7}{3m+1}$-approximation in polynomial time for $m \geq 4$ and $\frac{4}{3}$ for $m=3$. Our algorithm is based on a recursive scheduling approach where in each step we reduce the correlation in form of long chains. Our method adds to the rather short list of examples where hierarchies are actually useful to obtain better approximation algorithms.