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- Thorsten Ehlers, Florin Manea, Robert Mercas, Dirk Nowotka
- Developments in Language Theory
- 2014

Two words are called k-abelian equivalent, if they share the same multiplic-ities for all factors of length at most k. We present an optimal linear time algorithm for identifying all occurrences of factors in a text that are k-abelian equivalent to some pattern P. Moreover, an optimal algorithm for finding the largest k for which two words are k-abelian… (More)

- Thorsten Ehlers, Mike Müller
- CiE
- 2015

We present new parallel sorting networks for 17 to 20 inputs. For 17, 19, and 20 inputs these new networks are faster (i.e., they require less computation steps) than the previously known best networks. Therefore, we improve upon the known upper bounds for minimal depth sorting networks on 17, 19, and 20 channels. Furthermore, we show that our sorting… (More)

- Thorsten Ehlers, Mike Müller
- ArXiv
- 2014

We present new parallel sorting networks for 17 to 20 inputs. For 17, 19, and 20 inputs these new networks are faster (i.e., they require less computation steps) than the previously known best networks. Therefore , we improve upon the known upper bounds for minimal depth sorting networks on 17, 19, and 20 channels. The networks were obtained using a… (More)

- Ulf Rüegg, Thorsten Ehlers, Miro Spönemann, Reinhard von Hanxleden
- Graph Drawing
- 2016

The Directed Layering Problem (DLP) solves a step of the widely used layer-based approach to automatically draw directed acyclic graphs. To cater for cyclic graphs, usually a preprocessing step is used that solves the Feedback Arc Set Problem (FASP) to make the graph acyclic before a layering is determined. Here we present the Generalized Layering Problem… (More)

- Thorsten Ehlers, Dirk Nowotka, Philipp Sieweck, Johannes Traub
- Software Engineering
- 2014

This paper studies new properties of the front and back ends of a sorting network, and illustrates the utility of these in the search for new bounds on optimal sorting networks. Search focuses first on the " outsides " of the network and then on the inner part. All previous works focus only on properties of the front end of networks and on how to apply… (More)

- Thorsten Ehlers
- Inf. Process. Lett.
- 2017

- Thorsten Ehlers, Dirk Nowotka, Philipp Sieweck
- 2014 IEEE 26th International Conference on Tools…
- 2014

The exchange of learnt clauses is a key feature in parallel SAT solving. We present an approach based on a communication graph. Each solver thread corresponds to a node in this graph. Communication between two solvers is allowed if the respective nodes are connected by an edge. This yields another dimension in controlling the amount of communication. We… (More)

- Thorsten Ehlers, Klaus Jansen
- 2013 15th International Symposium on Symbolic and…
- 2013

We present a robust EPTAS for scheduling on identical machines. The running time for adding one job is bounded by 2<sup>O((1/ε2)</sup> log<sup>3(1/ε))</sup>. The migration factor required to gain a (1+ ε)-approximate schedule in each iteration is bounded by 2<sup>O((1/ε) log2(1/ε))</sup>.

- Thorsten Ehlers, Peter J. Stuckey
- CPAIOR
- 2016

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