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November 9 – 14 , 2014, Dagstuhl Seminar 14461

High-performance Graph Algorithms and Applications in Computational Science

Organizers

Ulrich Carsten Meyer (Goethe-Universität – Frankfurt a. M., DE)
Henning Meyerhenke (KIT – Karlsruher Institut für Technologie, DE)
Ali Pinar (Sandia Nat. Labs – Livermore, US)
Ilya Safro (Clemson University, US)

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Documents

Dagstuhl Report, Volume 4, Issue 11 Dagstuhl Report
Aims & Scope
List of Participants
Shared Documents
Dagstuhl Seminar Schedule [pdf]

Summary

Many presentations in this Dagstuhl seminar emphasized recent trends regarding typical inputs and their effect on graph algorithm development for practical purposes. One can divide these presentations into four categories: (i) Traditional graph (or matrix) problems in new scenarios, (ii) graph analytics algorithms of various sorts, (iii) parallel computing aspects such as tools, computational models, load balancing, and communication; and finally (iv) emerging high-performance application and hardware trends. The following four paragraphs give a brief overview over the talks presented in each of these categories.

Pothen discussed different matching problems and how the emergence of complex networks have changed various matching algorithms recently. Road networks, in turn, are by no means complex and the traditional Dijkstra algorithm solves queries on continental instances in few seconds. Yet, for more challenging scenarios, for example millions of queries per second on webservers or multiple optimization critieria, more elaborate solutions are necessary, as presented by Sanders. Toledo addressed the importance of communication efficiency on large-scale parallel systems for traditional numerical problems such as LU decomposition. A similar numerical topic was the solution of Laplacian linear systems, for which new combinatorial solvers and related techniques from the theory community were presented and discussed by Madry and by Toledo. Furthermore, Boman and Toledo initiated a tangible plan for a scientific competition on solvers for this class of linear systems.

The analytics algorithms part experienced a number of talks on graph clustering and community detection, which means the identification of natural vertex groups in graphs. Several very fast algorithms and their implementation were discussed and compared. Centralities are used for finding important (but in general unrelated) vertices or edges in a graph. Catalyürek showed how to exploit parallelism in centrality algorithms to speed them up in different hardware settings, including accelerators. Bergamini, in turn, used approximation to obtain a speedup in dynamic graphs. Many other analytics tasks and algorithms were discussed, including anomaly detection presented by Miller and label inference by Chakrabarti, who both focused on techniques for very large graphs. Graph size was also a motivation for sparsification as discussed by Parthasarathy, either to save space or running time (or both) in later stages of an algorithmic pipeline.

Parallelism was the common theme in the third category. Here we summarize algorithmic techniques such as load balancing by graph partitioning, computational models as well as tools and middleware. Several speakers outlined challenges and/or algorithmic solutions in graph partitioning, in particular for complex networks or massively parallel systems. It became also clear that the development of graph algorithms for massive inputs benefits from suitable computational models. An example is the parallel external memory model for which Meyer as well as Veith showed algorithmic solutions. Another prerequisite for efficient graph algorithms in practice is tool support, including building block standards (proposed by Buluc) and communication middleware (presented by Lumsdaine). The pros and cons of different tools were discussed in an animated manner with the co-located Dagstuhl seminar 14462 "Systems and Algorithms for Large-scale Graph Analytics" within a joint session. The organizers are confident that this discussion has led to a better understanding of each other's community and their contributions. We also hope and think that this exchange will lead to an accelerated dissemination of the respective leading research results across community borders.

Finally, Brugger presented innovative hardware specifically designed to support certain graph algorithms. Talks with a particular focus on innovative applications from outside the core of computer science were presented by several speakers as well. Both Srivastav and Buluc, for example, described algorithms for sequence assembly, a problem in bioinformatics with massive data sets.

License
  Creative Commons BY 3.0 Unported license
  Ulrich Carsten Meyer, Henning Meyerhenke, Ali Pinar, and Ilya Safro

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