## Section: New Results

### Scheduling series-parallel task graphs to minimize peak memory

Participants : Enver Kayaaslan, Thomas Lambert, Loris Marchal, Bora Uçar.

We consider a variant of the well-known, NP-complete problem of minimum cut linear arrangement for directed acyclic graphs. In this variant, we are given a directed acyclic graph and asked to find a topological ordering such that the maximum number of cut edges at any point in this ordering is minimum. In our main variant the vertices and edges have weights, and the aim is to minimize the maximum weight of cut edges in addition to the weight of the last vertex before the cut. There is a known, polynomial time algorithm [Liu, SIAM J. Algebra. Discr., 1987] for the cases where the input graph is a rooted tree. We focus on the variant where the input graph is a directed series-parallel graph, and propose a polynomial time algorithm. Directed acyclic graphs are used to model scientific applications where the vertices correspond to the tasks of a given application and the edges represent the dependencies between the tasks. In such models, the problem we address reads as minimizing the peak memory requirement in an execution of the application. Our work, combined with Liu’s work on rooted trees addresses this practical problem in two important classes of applications.

This work is described in a technical report [50].