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Documents authored by Strasser, Ben

Document
DOI: 10.4230/LIPIcs.SEA.2021.6
A Fast and Tight Heuristic for A* in Road Networks

Authors: Ben Strasser and Tim Zeitz

Published in: LIPIcs, Volume 190, 19th International Symposium on Experimental Algorithms (SEA 2021)

Abstract
We study exact, efficient and practical algorithms for route planning in large road networks. Routing applications often require integrating the current traffic situation, planning ahead with traffic predictions for the future, respecting forbidden turns, and many other features depending on the exact application. While Dijkstra’s algorithm can be used to solve these problems, it is too slow for many applications. A* is a classical approach to accelerate Dijkstra’s algorithm. A* can support many extended scenarios without much additional implementation complexity. However, A*’s performance depends on the availability of a good heuristic that estimates distances. Computing tight distance estimates is a challenge on its own. On road networks, shortest paths can also be quickly computed using hierarchical speedup techniques. They achieve speed and exactness but sacrifice A*’s flexibility. Extending them to certain practical applications can be hard. In this paper, we present an algorithm to efficiently extract distance estimates for A* from Contraction Hierarchies (CH), a hierarchical technique. We call our heuristic CH-Potentials. Our approach allows decoupling the supported extensions from the hierarchical speed-up technique. Additionally, we describe A* optimizations to accelerate the processing of low degree nodes, which often occur in road networks.
Cite as

Ben Strasser and Tim Zeitz. A Fast and Tight Heuristic for A* in Road Networks. In 19th International Symposium on Experimental Algorithms (SEA 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 190, pp. 6:1-6:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{strasser_et_al:LIPIcs.SEA.2021.6,
  author =	{Strasser, Ben and Zeitz, Tim},
  title =	{{A Fast and Tight Heuristic for A* in Road Networks}},
  booktitle =	{19th International Symposium on Experimental Algorithms (SEA 2021)},
  pages =	{6:1--6:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-185-6},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{190},
  editor =	{Coudert, David and Natale, Emanuele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2021.6},
  URN =		{urn:nbn:de:0030-drops-137780},
  doi =		{10.4230/LIPIcs.SEA.2021.6},
  annote =	{Keywords: route planning, shortest paths, realistic road networks}
}
Document
PACE Solver Description
DOI: 10.4230/LIPIcs.IPEC.2020.32
PACE Solver Description: Tree Depth with FlowCutter

Authors: Ben Strasser

Published in: LIPIcs, Volume 180, 15th International Symposium on Parameterized and Exact Computation (IPEC 2020)

Abstract
We describe the FlowCutter submission to the PACE 2020 heuristic tree-depth challenge. The task of the challenge consists of computing an elimination tree of small height for a given graph. At its core our submission uses a nested dissection approach, with FlowCutter as graph bisection algorithm.
Cite as

Ben Strasser. PACE Solver Description: Tree Depth with FlowCutter. In 15th International Symposium on Parameterized and Exact Computation (IPEC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 180, pp. 32:1-32:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{strasser:LIPIcs.IPEC.2020.32,
  author =	{Strasser, Ben},
  title =	{{PACE Solver Description: Tree Depth with FlowCutter}},
  booktitle =	{15th International Symposium on Parameterized and Exact Computation (IPEC 2020)},
  pages =	{32:1--32:4},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-172-6},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{180},
  editor =	{Cao, Yixin and Pilipczuk, Marcin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2020.32},
  URN =		{urn:nbn:de:0030-drops-133350},
  doi =		{10.4230/LIPIcs.IPEC.2020.32},
  annote =	{Keywords: tree depth, graph algorithm, partitioning}
}
Document
DOI: 10.4230/LIPIcs.ESA.2020.81
Space-Efficient, Fast and Exact Routing in Time-Dependent Road Networks

Authors: Ben Strasser, Dorothea Wagner, and Tim Zeitz

Published in: LIPIcs, Volume 173, 28th Annual European Symposium on Algorithms (ESA 2020)

Abstract
We study the problem of computing shortest paths in massive road networks with traffic predictions. Incorporating traffic predictions into routing allows, for example, to avoid commuter traffic congestions. Existing techniques follow a two-phase approach: In a preprocessing step, an index is built. The index depends on the road network and the traffic patterns but not on the path start and end. The latter are the input of the query phase, in which shortest paths are computed. All existing techniques have either large index size, slow query running times, or may compute suboptimal paths. In this work, we introduce CATCHUp (Customizable Approximated Time-dependent Contraction Hierarchies through Unpacking), the first algorithm that simultaneously achieves all three objectives. The core idea of CATCHUp is to store paths instead of travel times at shortcuts. Shortcut travel times are derived lazily from the stored paths. We perform an experimental study on a set of real world instances and compare our approach with state-of-the-art techniques. Our approach achieves the fastest preprocessing, competitive query running times and up to 30 times smaller indexes than competing approaches.
Cite as

Ben Strasser, Dorothea Wagner, and Tim Zeitz. Space-Efficient, Fast and Exact Routing in Time-Dependent Road Networks. In 28th Annual European Symposium on Algorithms (ESA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 173, pp. 81:1-81:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{strasser_et_al:LIPIcs.ESA.2020.81,
  author =	{Strasser, Ben and Wagner, Dorothea and Zeitz, Tim},
  title =	{{Space-Efficient, Fast and Exact Routing in Time-Dependent Road Networks}},
  booktitle =	{28th Annual European Symposium on Algorithms (ESA 2020)},
  pages =	{81:1--81:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-162-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{173},
  editor =	{Grandoni, Fabrizio and Herman, Grzegorz and Sanders, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2020.81},
  URN =		{urn:nbn:de:0030-drops-129479},
  doi =		{10.4230/LIPIcs.ESA.2020.81},
  annote =	{Keywords: realistic road networks, time-dependent route planning, shortest paths}
}
Document
DOI: 10.4230/LIPIcs.SEA.2020.10
Engineering Exact Quasi-Threshold Editing

Authors: Lars Gottesbüren, Michael Hamann, Philipp Schoch, Ben Strasser, Dorothea Wagner, and Sven Zühlsdorf

Published in: LIPIcs, Volume 160, 18th International Symposium on Experimental Algorithms (SEA 2020)

Abstract
Quasi-threshold graphs are {C₄, P₄}-free graphs, i.e., they do not contain any cycle or path of four nodes as an induced subgraph. We study the {C₄, P₄}-free editing problem, which is the problem of finding a minimum number of edge insertions or deletions to transform an input graph into a quasi-threshold graph. This problem is NP-hard but fixed-parameter tractable (FPT) in the number of edits by using a branch-and-bound algorithm and admits a simple integer linear programming formulation (ILP). Both methods are also applicable to the general ℱ-free editing problem for any finite set of graphs ℱ. For the FPT algorithm, we introduce a fast heuristic for computing high-quality lower bounds and an improved branching strategy. For the ILP, we engineer several variants of row generation. We evaluate both methods for quasi-threshold editing on a large set of protein similarity graphs. For most instances, our optimizations speed up the FPT algorithm by one to three orders of magnitude. The running time of the ILP, that we solve using Gurobi, becomes only slightly faster. With all optimizations, the FPT algorithm is slightly faster than the ILP, even when listing all solutions. Additionally, we show that for almost all graphs, solutions of the previously proposed quasi-threshold editing heuristic QTM are close to optimal.
Cite as

Lars Gottesbüren, Michael Hamann, Philipp Schoch, Ben Strasser, Dorothea Wagner, and Sven Zühlsdorf. Engineering Exact Quasi-Threshold Editing. In 18th International Symposium on Experimental Algorithms (SEA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 160, pp. 10:1-10:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{gottesburen_et_al:LIPIcs.SEA.2020.10,
  author =	{Gottesb\"{u}ren, Lars and Hamann, Michael and Schoch, Philipp and Strasser, Ben and Wagner, Dorothea and Z\"{u}hlsdorf, Sven},
  title =	{{Engineering Exact Quasi-Threshold Editing}},
  booktitle =	{18th International Symposium on Experimental Algorithms (SEA 2020)},
  pages =	{10:1--10:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-148-1},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{160},
  editor =	{Faro, Simone and Cantone, Domenico},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2020.10},
  URN =		{urn:nbn:de:0030-drops-120849},
  doi =		{10.4230/LIPIcs.SEA.2020.10},
  annote =	{Keywords: Edge Editing, Integer Linear Programming, FPT algorithm, Quasi-Threshold Editing}
}
Document
DOI: 10.4230/OASIcs.ATMOS.2017.3
Dynamic Time-Dependent Routing in Road Networks Through Sampling

Authors: Ben Strasser

Published in: OASIcs, Volume 59, 17th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2017)

Abstract
We study the earliest arrival and profile problems in road networks with time-dependent functions as arc weights and dynamic updates. We present and experimentally evaluate simple, sampling-based, heuristic algorithms. Our evaluation is performed on large, current, production-grade road graph data with time-dependent arc weights. It clearly shows that the proposed algorithms are fast and compute paths with a sufficiently small error for most practical applications. We experimentally compare our algorithm against the current state-of-the-art. Our experiments reveal, that the memory consumption of existing algorithms is prohibitive on large instances. Our approach does not suffer from this limitation. Further, our algorithm is the only competitor able to answer profile queries on all test instances below 50ms. As our algorithm is simple to implement, we believe that it is a good fit for many realworld applications.
Cite as

Ben Strasser. Dynamic Time-Dependent Routing in Road Networks Through Sampling. In 17th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2017). Open Access Series in Informatics (OASIcs), Volume 59, pp. 3:1-3:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{strasser:OASIcs.ATMOS.2017.3,
  author =	{Strasser, Ben},
  title =	{{Dynamic Time-Dependent Routing in Road Networks Through Sampling}},
  booktitle =	{17th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2017)},
  pages =	{3:1--3:17},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-042-2},
  ISSN =	{2190-6807},
  year =	{2017},
  volume =	{59},
  editor =	{D'Angelo, Gianlorenzo and Dollevoet, Twan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2017.3},
  URN =		{urn:nbn:de:0030-drops-78972},
  doi =		{10.4230/OASIcs.ATMOS.2017.3},
  annote =	{Keywords: shortest path, time-dependent, road graphs, preprocessing}
}
Document
DOI: 10.4230/LIPIcs.SEA.2017.20
Efficient Traffic Assignment for Public Transit Networks

Authors: Lars Briem, Sebastian Buck, Holger Ebhart, Nicolai Mallig, Ben Strasser, Peter Vortisch, Dorothea Wagner, and Tobias Zündorf

Published in: LIPIcs, Volume 75, 16th International Symposium on Experimental Algorithms (SEA 2017)

Abstract
We study the problem of computing traffic assignments for public transit networks: Given a public transit network and a demand (i.e. a list of passengers, each with associated origin, destination, and departure time), the objective is to compute the utilization of every vehicle. Efficient assignment algorithms are a core component of many urban traffic planning tools. In this work, we present a novel algorithm for computing public transit assignments. Our approach is based upon a microscopic Monte Carlo simulation of individual passengers. In order to model realistic passenger behavior, we base all routing decisions on travel time, number of transfers, time spent walking or waiting, and delay robustness. We show how several passengers can be processed during a single scan of the network, based on the Connection Scan Algorithm [Dibbelt et al., LNCS Springer 2013], resulting in a highly efficient algorithm. We conclude with an experimental study, showing that our assignments are comparable in terms of quality to the state-of-the-art. Using the parallelized version of our algorithm, we are able to compute a traffic assignment for more than ten million passengers in well below a minute, which outperforms previous works by more than an order of magnitude.
Cite as

Lars Briem, Sebastian Buck, Holger Ebhart, Nicolai Mallig, Ben Strasser, Peter Vortisch, Dorothea Wagner, and Tobias Zündorf. Efficient Traffic Assignment for Public Transit Networks. In 16th International Symposium on Experimental Algorithms (SEA 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 75, pp. 20:1-20:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{briem_et_al:LIPIcs.SEA.2017.20,
  author =	{Briem, Lars and Buck, Sebastian and Ebhart, Holger and Mallig, Nicolai and Strasser, Ben and Vortisch, Peter and Wagner, Dorothea and Z\"{u}ndorf, Tobias},
  title =	{{Efficient Traffic Assignment for Public Transit Networks}},
  booktitle =	{16th International Symposium on Experimental Algorithms (SEA 2017)},
  pages =	{20:1--20:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-036-1},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{75},
  editor =	{Iliopoulos, Costas S. and Pissis, Solon P. and Puglisi, Simon J. and Raman, Rajeev},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2017.20},
  URN =		{urn:nbn:de:0030-drops-76109},
  doi =		{10.4230/LIPIcs.SEA.2017.20},
  annote =	{Keywords: Algorithms, Optimization, Route planning, Public transportation}
}
Document
DOI: 10.4230/OASIcs.ATMOS.2014.1
Delay-Robust Journeys in Timetable Networks with Minimum Expected Arrival Time

Authors: Julian Dibbelt, Ben Strasser, and Dorothea Wagner

Published in: OASIcs, Volume 42, 14th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (2014)

Abstract
We study the problem of computing delay-robust routes in timetable networks. Instead of a single path we compute a decision graph containing all stops and trains/vehicles that might be relevant. Delays are formalized using a stochastic model. We show how to compute a decision graph that minimizes the expected arrival time while bounding the latest arrival time over all sub-paths. Finally we show how the information contained within a decision graph can compactly be represented to the user. We experimentally evaluate our algorithms and show that the running times allow for interactive usage on a realistic train network.
Cite as

Julian Dibbelt, Ben Strasser, and Dorothea Wagner. Delay-Robust Journeys in Timetable Networks with Minimum Expected Arrival Time. In 14th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems. Open Access Series in Informatics (OASIcs), Volume 42, pp. 1-14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{dibbelt_et_al:OASIcs.ATMOS.2014.1,
  author =	{Dibbelt, Julian and Strasser, Ben and Wagner, Dorothea},
  title =	{{Delay-Robust Journeys in Timetable Networks with Minimum Expected Arrival Time}},
  booktitle =	{14th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems},
  pages =	{1--14},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-75-0},
  ISSN =	{2190-6807},
  year =	{2014},
  volume =	{42},
  editor =	{Funke, Stefan and Mihal\'{a}k, Mat\'{u}s},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2014.1},
  URN =		{urn:nbn:de:0030-drops-47488},
  doi =		{10.4230/OASIcs.ATMOS.2014.1},
  annote =	{Keywords: Algorithms, Optimization, Delay-robustness, Route planning, Public transportation}
}
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