TY - JOUR A1 - Heinze, Rieke A1 - Dipankar, Anurag A1 - Henken, Cintia Carbajal A1 - Moseley, Christopher A1 - Sourdeval, Odran A1 - Trömel, Silke A1 - Xie, Xinxin A1 - Adamidis, Panos A1 - Ament, Felix A1 - Baars, Holger A1 - Barthlott, Christian A1 - Behrendt, Andreas A1 - Blahak, Ulrich A1 - Bley, Sebastian A1 - Brdar, Slavko A1 - Brueck, Matthias A1 - Crewell, Susanne A1 - Deneke, Hartwig A1 - Di Girolamo, Paolo A1 - Evaristo, Raquel A1 - Fischer, Jürgen A1 - Frank, Christopher A1 - Friederichs, Petra A1 - Göcke, Tobias A1 - Gorges, Ksenia A1 - Hande, Luke A1 - Hanke, Moritz A1 - Hansen, Akio A1 - Hege, Hans-Christian A1 - Hose, Corinna A1 - Jahns, Thomas A1 - Kalthoff, Norbert A1 - Klocke, Daniel A1 - Kneifel, Stefan A1 - Knippertz, Peter A1 - Kuhn, Alexander A1 - van Laar, Thriza A1 - Macke, Andreas A1 - Maurer, Vera A1 - Mayer, Bernhard A1 - Meyer, Catrin I. A1 - Muppa, Shravan K. A1 - Neggers, Roeland A. J. A1 - Orlandi, Emiliano A1 - Pantillon, Florian A1 - Pospichal, Bernhard A1 - Röber, Niklas A1 - Scheck, Leonhard A1 - Seifert, Axel A1 - Seifert, Patric A1 - Senf, Fabian A1 - Siligam, Pavan A1 - Simmer, Clemens A1 - Steinke, Sandra A1 - Stevens, Bjorn A1 - Wapler, Kathrin A1 - Weniger, Michael A1 - Wulfmeyer, Volker A1 - Zängl, Günther A1 - Zhang, Dan A1 - Quaas, Johannes T1 - Large-eddy simulations over Germany using ICON: a comprehensive evaluation JF - Quarterly Journal of the Royal Meteorological Society N2 - Large-eddy simulations (LES) with the new ICOsahedral Non-hydrostatic atmosphere model (ICON) covering Germany are evaluated for four days in spring 2013 using observational data from various sources. Reference simulations with the established Consortium for Small-scale Modelling (COSMO) numerical weather prediction model and further standard LES codes are performed and used as a reference. This comprehensive evaluation approach covers multiple parameters and scales, focusing on boundary-layer variables, clouds and precipitation. The evaluation points to the need to work on parametrizations influencing the surface energy balance, and possibly on ice cloud microphysics. The central purpose for the development and application of ICON in the LES configuration is the use of simulation results to improve the understanding of moist processes, as well as their parametrization in climate models. The evaluation thus aims at building confidence in the model's ability to simulate small- to mesoscale variability in turbulence, clouds and precipitation. The results are encouraging: the high-resolution model matches the observed variability much better at small- to mesoscales than the coarser resolved reference model. In its highest grid resolution, the simulated turbulence profiles are realistic and column water vapour matches the observed temporal variability at short time-scales. Despite being somewhat too large and too frequent, small cumulus clouds are well represented in comparison with satellite data, as is the shape of the cloud size spectrum. Variability of cloud water matches the satellite observations much better in ICON than in the reference model. In this sense, it is concluded that the model is fit for the purpose of using its output for parametrization development, despite the potential to improve further some important aspects of processes that are also parametrized in the high-resolution model. Y1 - 2017 U6 - https://doi.org/10.1002/qj.2947 VL - 143 IS - 702 SP - 69 EP - 100 ER - TY - GEN A1 - Werner, Axel A1 - Aurzada, Frank A1 - Bley, Andreas A1 - Eisenblätter, Andreas A1 - Geerdes, Hans-Florian A1 - Guillemard, Mijail A1 - Kutyniok, Gitta A1 - Philipp, Friedrich A1 - Raack, Christian A1 - Scheutzow, Michael ED - Deuflhard, Peter ED - Grötschel, Martin ED - Hömberg, Dietmar ED - Horst, Ulrich ED - Kramer, Jürg ED - Mehrmann, Volker ED - Polthier, Konrad ED - Schmidt, Frank ED - Schütte, Christof ED - Skutella, Martin ED - Sprekels, Jürgen T1 - Mathematics for telecommunications T2 - MATHEON - Mathematics for Key Technologies Y1 - 2014 U6 - https://doi.org/10.4171/137 VL - 1 SP - 75 EP - 89 PB - European Mathematical Society ET - EMS Series in Industrial and Applied Mathematics ER - TY - GEN A1 - Bley, Andreas A1 - Koch, Thorsten A1 - Wessäly, Roland T1 - Large-scale hierarchical networks: How to compute an optimal architecture? N2 - In this article, we present a mathematical model and an algorithm to support one of the central strategic planning decisions of network operators: How to organize a large number of locations into a hierarchical network? We propose a solution approach that is based on mixed-integer programming and Lagrangian relaxation techniques. As major advantage, our approach provides not only solutions but also worst-case quality guarantees. Real-world scenarios with more than 750 locations have been solved within 30 minutes to less than 1\% off optimality. T3 - ZIB-Report - 04-04 KW - Hierarchical Networks KW - Mixed-Integer Programming KW - Lagrangian Relaxation Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-7799 ER - TY - GEN A1 - Bley, Andreas T1 - Approximability of Unsplittable Shortest Path Routing Problems N2 - In this paper, we discuss the relation of unsplittable shortest path routing (USPR) to other routing schemes and study the approximability of three USPR network planning problems. Given a digraph $D=(V,A)$ and a set $K$ of directed commodities, an USPR is a set of flow paths $\Phi_{(s,t)}$, $(s,t)\in K$, such that there exists a metric $\lambda=(\lambda_a)\in \mathbb{Z}^A_+$ with respect to which each $\Phi_{(s,t)}$ is the unique shortest $(s,t)$-path. In the \textsc{Min-Con-USPR} problem, we seek for an USPR that minimizes the maximum congestion over all arcs. We show that this problem is hard to approximate within a factor of $\mathcal{O}(|V|^{1-\epsilon})$, but easily approximable within min$(|A|,|K|)$ in general and within $\mathcal{O}(1)$ if the underlying graph is an undirected cycle or a bidirected ring. We also construct examples where the minimum congestion that can be obtained by USPR is a factor of $\Omega(|V|^2)$ larger than that achievable by unsplittable flow routing or by shortest multi-path routing, and a factor of $\Omega(|V|)$ larger than by unsplittable source-invariant routing. In the CAP-USPR problem, we seek for a minimum cost installation of integer arc capacities that admit an USPR of the given commodities. We prove that this problem is $\mathcal{NP}$-hard to approximate within $2-\epsilon$ (even in the undirected case), and we devise approximation algorithms for various special cases. The fixed charge network design problem \textsc{Cap-USPR}, where the task is to find a minimum cost subgraph of $D$ whose fixed arc capacities admit an USPR of the commodities, is shown to be $\mathcal{NPO}$-complete. All three problems are of great practical interest in the planning of telecommunication networks that are based on shortest path routing protocols. Our results indicate that they are harder than the corresponding unsplittable flow or shortest multi-path routing problems. T3 - ZIB-Report - 06-02 KW - Shortest path routing KW - unsplittable flow KW - computational complexity KW - approximation Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-8968 ER - TY - GEN A1 - Bley, Andreas A1 - Pattloch, Marcus T1 - Modellierung und Optimierung der X-WiN Plattform N2 - In diesem Artikel werden die Optimierungsmodelle und -verfahren beschrieben, die bei der Planung des Kernnetzes und der Zugangsinfrastruktur des X-WiN verwendet wurden. T3 - ZIB-Report - 05-21 Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-8551 ER - TY - CHAP A1 - Bley, Andreas A1 - Koch, Thorsten A1 - Wessäly, Roland ED - Kaindl, H. T1 - Large-Scale hierarchical networks: How to compute an optimal architecture? T2 - Networks 2004 Y1 - 2004 SN - 3-8007-2840-0 SP - 429 EP - 434 PB - VDE Verlag CY - Berlin ER - TY - GEN A1 - Bley, Andreas T1 - On the Complexity of Vertex-Disjoint Length-Restricted Path Problems N2 - Let $G=(V,E)$ be a simple graph and $s$ and $t$ be two distinct vertices of $G$. A path in $G$ is called $\ell$-bounded for some $\ell\in\mathbb{N}$, if it does not contain more than $\ell$ edges. We study the computational complexity of approximating the optimum value for two optimization problems of finding sets of vertex-disjoint $\ell$-bounded $s,t$-paths in $G$. First, we show that computing the maximum number of vertex-disjoint $\ell$-bounded $s,t$-paths is $\mathcal{AP\kern-1pt X}$--complete for any fixed length bound $\ell\geq 5$. Second, for a given number $k\in\mathbb{N}$, $1\leq k \leq |V|-1$, and non-negative weights on the edges of $G$, the problem of finding $k$ vertex-disjoint $\ell$-bounded $s,t$-paths with minimal total weight is proven to be $\mathcal{NPO}$--complete for any length bound $\ell\geq 5$. Furthermore, we show that, even if $G$ is complete, it is $\mathcal{NP}$--complete to approximate the optimal solution value of this problem within a factor of $2^{\langle\phi\rangle^\epsilon}$ for any constant $0<\epsilon<1$, where $\langle\phi\rangle$ denotes the encoding size of the given problem instance $\phi$. We prove that these results are tight in the sense that for lengths $\ell\leq 4$ both problems are polynomially solvable, assuming that the weights satisfy a generalized triangle inequality in the weighted problem. All results presented also hold for directed and non-simple graphs. For the analogous problems where the path length restriction is replaced by the condition that all paths must have length equal to $\ell$ or where vertex-disjointness is replaced by edge-disjointness we obtain similar results. T3 - ZIB-Report - SC-98-20 KW - disjoint paths KW - length bounded paths KW - approximation KW - reducibility KW - completeness Y1 - 1998 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-3639 ER - TY - GEN A1 - Bley, Andreas A1 - Grötschel, Martin A1 - Wessäly, Roland T1 - Design of Broadband Virtual Private Networks: Model and Heuristics for the B–WiN N2 - We investigate the problem of designing survivable broadband virtual private networks that employ the Open Shortest Path First (OSPF) routing protocol to route the packages. The capacities available for the links of the network are a minimal capacity plus multiples of a unit capacity. Given the directed communication demands between all pairs of nodes, we wish to select the capacities in a such way, that even in case of a single node or a single link failure a specified percentage of each demand can be satisfied and the costs for these capacities are minimal. We present a mixed--integer linear programming formulation of this problem and several heuristics for its solution. Furthermore, we report on computational results with real-world data. T3 - ZIB-Report - SC-98-13 KW - Telecommunication Network Design KW - Survivable Networks KW - Network Capacity Planning KW - OSPF Routing KW - Shortest Path Routing KW - Heuristics Y1 - 1998 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-3565 ER - TY - CHAP A1 - Bley, Andreas A1 - Gleixner, Ambros A1 - Koch, Thorsten A1 - Vigerske, Stefan T1 - Comparing MIQCP Solvers to a Specialised Algorithm for Mine Production Scheduling T2 - Modeling, Simulation and Optimization of Complex Processes. Proceedings of the Fourth International Conference on High Performance Scientific Computing, March 2-6, 2009, Hanoi, Vietnam N2 - In this paper we investigate the performance of several out-of-the box solvers for mixed-integer quadratically constrained programmes (MIQCPs) on an open pit mine production scheduling problem with mixing constraints. We compare the solvers BARON, Couenne, SBB, and SCIP to a problem-specific algorithm on two different MIQCP formulations. The computational results presented show that general-purpose solvers with no particular knowledge of problem structure are able to nearly match the performance of a hand-crafted algorithm. Y1 - 2012 U6 - https://doi.org/10.1007/978-3-642-25707-0_3 SP - 25 EP - 39 ER - TY - GEN A1 - Bley, Andreas A1 - Gleixner, Ambros A1 - Koch, Thorsten A1 - Vigerske, Stefan T1 - Comparing MIQCP solvers to a specialised algorithm for mine production scheduling N2 - In this paper we investigate the performance of several out-of-the box solvers for mixed-integer quadratically constrained programmes (MIQCPs) on an open pit mine production scheduling problem with mixing constraints. We compare the solvers BARON, Couenne, SBB, and SCIP to a problem-specific algorithm on two different MIQCP formulations. The computational results presented show that general-purpose solvers with no particular knowledge of problem structure are able to nearly match the performance of a hand-crafted algorithm. T3 - ZIB-Report - 09-32 Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-11507 SN - 1438-0064 ER -