TY - GEN A1 - Rambau, Jörg T1 - Circuit Admissible Triangulations of Oriented Matroids N2 - All triangulations of euclidean oriented matroids are of the same PL-homeomorphism type by a result of Anderson. That means all triangulations of euclidean acyclic oriented matroids are PL-homeomorphic to PL-balls and that all triangulations of totally cyclic oriented matroids are PL-homeomorphic to PL-spheres. For non-euclidean oriented matroids this question is wide open. One key point in the proof of Anderson is the following fact: for every triangulation of a euclidean oriented matroid the adjacency graph of the set of all simplices ``intersecting'' a segment $[p_-p_+]$ is a path. We call this graph the $[p_-p_+]$-adjacency graph of the triangulation. While we cannot solve the problem of the topological type of triangulations of general oriented matroids we show in this note that for every circuit admissible triangulation of an arbitrary oriented matroid the $[p_-p_+]$-adjacency graph is a path. T3 - ZIB-Report - 00-45 KW - triangulations of oriented matroids KW - topological type KW - segment adjacency graph Y1 - 2000 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6139 ER - TY - GEN A1 - Rambau, Jörg T1 - Triangulierungen von Punktmengen und Polyedern N2 - Dieser Report wurde im Sommersemester 2000 an der TU Berlin in einer Spezialvorlesung über Triangulierungen von Punktmengen und Polyedern als Skriptum verwendet. Nach einem motivierenden Kapitel werden grundlegende Begriffe und Konstruktionen in der Theorie der Triangulierungen von Punktmengen und Polyedern vorgestellt. Danach werden als weiterführende Themen reguläre Triangulierungen, Sekundärpolytope, bistellare Operationen, höhere Stasheff-Tamari-Halbordnungen und Triangulierungen mit wenigen bzw. gar keinen Flips behandelt. Ein Kapitel über Enumeration und Optimierung beschließt die Zusammenstellung. T3 - ZIB-Report - 00-46 KW - point configuration KW - triangulation KW - polytope KW - polyhedron KW - Gale diagram KW - secondary polytope KW - cyclic polytope KW - graph of all triangulations KW - conn Y1 - 2000 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6145 ER - TY - GEN A1 - Hülsermann, Ralf A1 - Jäger, Monika A1 - Krumke, Sven A1 - Poensgen, Diana A1 - Rambau, Jörg A1 - Tuchscherer, Andreas T1 - Dynamic Routing Algorithms in Transparent Optical Networks An Experimental Study Based on Real Data N2 - Today's telecommunication networks are configured statically. Whenever a connection is established, the customer has permanent access to it. However, it is observed that usually the connection is not used continuously. At this point, dynamic provisioning could increase the utilization of network resources. WDM based Optical Transport Networks (OTNs) will shortly allow for fast dynamic network reconfiguration. This enables optical broadband leased line services on demand. Since service requests competing for network resources may lead to service blocking, it is vital to use appropriate strategies for routing and wavelength assignment in transparent optical networks. We simulate the service blocking probabilities of various dynamic algorithms for this problem using a well-founded traffic model for two realistic networks. One of the algorithms using shortest path routings performs best on all instances. Surprisingly, the tie-breaking rule between equally short paths in different wavelengths decides between success or failure. T3 - ZIB-Report - 02-35 KW - Dynamic Network Configuration KW - Routing and Wavelength Allocation KW - Transparent Optical Networks KW - Blocking Probability KW - Simulation Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-7025 ER - TY - GEN A1 - Rambau, Jörg T1 - TOPCOM: Triangulations of Point Configurations and Oriented Matroids N2 - TOPCOM is a package for computing triangulations of point configurations and oriented matroids. For example, for a point configuration one can compute the chirotope, components of the flip graph of triangulations, enumerate all triangulations. The core algorithms implemented in TOPCOM are described, and implentation issues are discussed. T3 - ZIB-Report - 02-17 KW - triangulation KW - point configuration KW - oriented matroid KW - software KW - chirotope KW - circuit KW - cocircuit KW - symmetry KW - TOPCOM Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6849 ER - TY - GEN A1 - Grötschel, Martin A1 - Krumke, Sven A1 - Rambau, Jörg A1 - Torres, Luis Miguel T1 - Making the Yellow Angels Fly: Online Dispatching Of Service Vehicles in Real Time N2 - Combinatorial online optimization is an area with lots of applications and potential for significant progress, both in theory and practice. In this short note we sketch the ADACproblem, a typical large-scale online optimization problem, discuss some theoretical and pratical issues coming up, and explain, very briefly, how we approach this problem mathematically. Online problems are a battlefield of heuristics with many strong claims about their solution quality. We indicate that a stronger problem orientation and the use of a little more mathematics may yield. T3 - ZIB-Report - 02-18 KW - vehicle dispatching KW - soft time windows KW - real-time KW - column generation KW - pricing KW - branch and bound KW - real world data KW - ADAC Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6858 ER - TY - GEN A1 - Krumke, Sven A1 - Lipmann, Maarten A1 - Paepe, Willem de A1 - Poensgen, Diana A1 - Rambau, Jörg A1 - Stougie, Leen A1 - Woeginger, Gerhard T1 - How to Cut a Cake Almost Fairly N2 - In the cake cutting problem, $n\ge2$ players want to cut a cake into $n$ pieces so that every player gets a ``fair'' share of the cake by his own measure. We describe a protocol with $n-1$~cuts in which each player can enforce to get a share of at least~$1/(2n-2)$. Moreover we show that no protocol with $n-1$~cuts can guarantee a better fraction. T3 - ZIB-Report - 02-23 KW - Fair division KW - cake cutting Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6905 ER - TY - GEN A1 - Grötschel, Martin A1 - Krumke, Sven A1 - Rambau, Jörg A1 - Winter, Thomas A1 - Zimmermann, Uwe T1 - Combinatorial Online Optimization in Real Time N2 - Optimization is the task of finding an optimum solution to a given problem. When the decision variables are discrete we speak of a combinatorial optimization problem. Such a problem is online when decisions have to be made before all data of the problem are known. And we speak of a real-time online problem when online decisions have to be computed within very tight time bounds. This paper surveys the are of combinatorial online and real-time optimization, it discusses, in particular, the concepts with which online and real-time algorithms can be analyzed. T3 - ZIB-Report - 01-16 KW - Online Optimization KW - Realtime Optimization KW - Competitive Analysis KW - Heuristics KW - Survey Y1 - 2001 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6424 ER - TY - GEN A1 - Grötschel, Martin A1 - Krumke, Sven A1 - Rambau, Jörg T1 - Online Optimization of Complex Transportation Systems N2 - This paper discusses online optimization of real-world transportation systems. We concentrate on transportation problems arising in production and manufacturing processes, in particular in company internal logistics. We describe basic techniques to design online optimization algorithms for such systems, but our main focus is decision support for the planner: which online algorithm is the most appropriate one in a particular setting? We show by means of several examples that traditional methods for the evaluation of online algorithms often do not suffice to judge the strengths and weaknesses of online algorithms. We present modifications of well-known evaluation techniques and some new methods, and we argue that the selection of an online algorithm to be employed in practice should be based on a sound combination of several theoretical and practical evaluation criteria, including simulation. T3 - ZIB-Report - 01-17 Y1 - 2001 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6438 ER - TY - GEN A1 - Krumke, Sven A1 - Rambau, Jörg A1 - Torres, Luis Miguel T1 - Real-Time Dispatching of Guided and Unguided Automobile Service Units with Soft Time Windows N2 - Given a set of service requests (events), a set of guided servers (units), and a set of unguided service contractors (conts), the vehicle dispatching problem {\sl vdp} is the task to find an assignment of events to units and conts as well as tours for all units starting at their current positions and ending at their home positions (dispatch) such that the total cost of the dispatch is minimized. The cost of a dispatch is the sum of unit costs, cont costs, and event costs. Unit costs consist of driving costs, service costs and overtime costs; cont costs consist of a fixed cost per service; event costs consist of late costs linear in the late time, which occur whenever the service of the event starts later than its deadline. The program \textsf{ZIBDIP} based on dynamic column generation and set partitioning yields solutions on heavy-load real-world instances (215 events, 95 units) in less than a minute that are no worse than 1\% from optimum on state-of-the-art personal computers. T3 - ZIB-Report - 01-22 KW - vehicle dispatching KW - soft time windows KW - real-time KW - column generation KW - pricing KW - branch and bound KW - real world data KW - ADAC Y1 - 2001 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6484 ER - TY - GEN A1 - Krumke, Sven A1 - Paepe, Willem de A1 - Rambau, Jörg A1 - Stougie, Leen T1 - Online Bin-Coloring N2 - We introduce a new problem that was motivated by a (more complicated) problem arising in a robotized assembly enviroment. The bin coloring problem is to pack unit size colored items into bins, such that the maximum number of different colors per bin is minimized. Each bin has size~$B\in\mathbb{N}$. The packing process is subject to the constraint that at any moment in time at most $q\in\mathbb{N}$ bins may be partially filled. Moreover, bins may only be closed if they are filled completely. An online algorithm must pack each item must be packed without knowledge of any future items. We investigate the existence of competitive online algorithms for the online uniform binpacking problem. We show upper bounds for the bin coloring problem. We prove an upper bound of $3q$ - 1 and a lower bound of $2q$ for the competitive ratio of a natural greedy-type algorithm, and show that surprisingly a trivial algorithm which uses only one open bin has a strictly better competitive ratio of $2q$ - 1. Morever, we show that any deterministic algorithm has a competitive ratio $\Omega (q)$ and that randomization does not improve this lower bound even when the adversary is oblivious. T3 - ZIB-Report - 01-07 KW - Online Optimization KW - randomized algorithms KW - lower bounds KW - competitive analysis Y1 - 2001 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6338 ER - TY - GEN A1 - Friese, Philipp A1 - Rambau, Jörg T1 - Online-Optimization of Multi-Elevator Transport Systems with Reoptimization Algorithms based on Set-Partitioning Models N2 - We develop and experimentally compare policies for the control of a system of $k$ elevators with capacity one in a transport environment with $\ell$ floors, an idealized version of a pallet elevator system in a large distribution center of the Herlitz PBS AG in Falkensee. Each elevator in the idealized system has an individual waiting queue of infinite capacity. On each floor, requests arrive over time in global waiting queues of infinite capacity. The goal is to find a policy that, without any knowledge about future requests, assigns an elevator to each req uest and a schedule to each elevator so that certain expected cost functions (e.g., the average or the maximal flow times) are minimized. We show that a reoptimization policy for minimizing average sq uared waiting times can be implemented to run in real-time ($1\,s$) using dynamic column generation. Moreover, in discrete event simulations with Poisson input it outperforms other commonly used polic ies like multi-server variants of greedy and nearest neighbor. T3 - ZIB-Report - 05-03 KW - elevator group control KW - policy KW - reoptimization KW - online KW - real-time KW - simulation Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-8373 ER - TY - GEN A1 - Pfeifle, Julian A1 - Rambau, Jörg T1 - Computing Triangulations Using Oriented Matroids N2 - Oriented matroids are combinatorial structures that encode the combinatorics of point configurations. The set of all triangulations of a point configuration depends only on its oriented matroid. We survey the most important ingredients necessary to exploit oriented matroids as a data structure for computing all triangulations of a point configuration, and report on experience with an implementation of these concepts in the software package TOPCOM. Next, we briefly overview the construction and an application of the secondary polytope of a point configuration, and calculate some examples illustrating how our tools were integrated into the {\sc polymake} framework. T3 - ZIB-Report - 02-02 KW - triangulation KW - oriented matroid KW - software KW - chirotope KW - circuit KW - cocircuit KW - symmetry KW - regular KW - secondary polytope KW - hypergeometric function Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-6692 ER - TY - GEN A1 - Krumke, Sven A1 - Rambau, Jörg A1 - Torres, Luis Miguel T1 - Online-Dispatching of Automobile Service Units N2 - We present an online algorithm for a real-world vehicle dispatching problem at ADAC, the German Automobile Association. T3 - ZIB-Report - 02-44 KW - vehicle dispatching KW - soft time windows KW - online KW - real-time KW - ADAC Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-7117 ER - TY - GEN A1 - Hiller, Benjamin A1 - Krumke, Sven A1 - Rambau, Jörg T1 - Reoptimization Gaps versus Model Errors in Online-Dispatching of Service Units for ADAC N2 - Under high load, the automated dispatching of service vehicles for the German Automobile Association (ADAC) must reoptimize a dispatch for 100--150 vehicles and 400 requests in about ten seconds to near optimality. In the presence of service contractors, this can be achieved by the column generation algorithm ZIBDIP. In metropolitan areas, however, service contractors cannot be dispatched automatically because they may decline. The problem: a model without contractors yields larger optimality gaps within ten seconds. One way-out are simplified reoptimization models. These compute a short-term dispatch containing only some of the requests: unknown future requests will influence future service anyway. The simpler the models the better the gaps, but also the larger the model error. What is more significant: reoptimization gap or reoptimization model error? We answer this question in simulations on real-world ADAC data: only the new model ZIBDIP{\footnotesize dummy} can keep up with ZIBDIP. T3 - ZIB-Report - 04-17 KW - vehicle dispatching KW - soft time windows KW - online KW - real-time KW - ADAC KW - optimality gap KW - high load Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-7928 ER - TY - GEN A1 - Athanasiadis, Christos A. A1 - Rambau, Jörg A1 - Santos, Francisco T1 - The Generalized Baues Problem for Cyclic Polytopes II N2 - Given an affine surjection of polytopes $\pi: P \to Q$, the Generalized Baues Problem asks whether the poset of all proper polyhedral subdivisions of $Q$ which are induced by the map $\pi$ has the homotopy type of a sphere. We extend earlier work of the last two authors on subdivisions of cyclic polytopes to give an affirmative answer to the problem for the natural surjections between cyclic polytopes $\pi: C(n,d') \to C(n,d)$ for all $1 \leq d < d' < n$. T3 - ZIB-Report - SC-98-43 KW - Generalized Baues Problem KW - Polyhedral Subdivisions KW - Induced Subdivisions KW - Poset KW - Spherical KW - Cyclic Polytopes KW - Bistellar Operations Y1 - 1999 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-3862 ER - TY - GEN A1 - Huber, Birkett A1 - Rambau, Jörg A1 - Santos, Francisco T1 - The Cayley Trick, lifting subdivisions and the Bohne-Dress theorem on zonotopal tilings N2 - In 1994, Sturmfels gave a polyhedral version of the Cayley Trick of elimination theory: he established an order-preserving bijection between the posets of \emph{coherent} mixed subdivisions of a Minkowski sum $\mathcal{A}_1+\cdots+\mathcal{A}_r$ of point configurations and of \emph{coherent} polyhedral subdivisions of the associated Cayley embedding $\mathcal{C}(\mathcal{A}_1,\dots,\mathcal{A}_r)$. In this paper we extend this correspondence in a natural way to cover also \emph{non-coherent} subdivisions. As an application, we show that the Cayley Trick combined with results of Santos on subdivisions of Lawrence polytopes provides a new independent proof of the Bohne-Dress Theorem on zonotopal tilings. This application uses a combinatorial characterization of lifting subdivisions, also originally proved by Santos. T3 - ZIB-Report - SC-98-44 KW - Polyhedral subdivision KW - fiber polytope KW - mixed subdivision KW - lifting subdivision KW - Minkowski sum KW - Cayley Trick KW - Bohne-Dress Theorem Y1 - 1999 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-3874 ER - TY - GEN A1 - Heinz, Stefan A1 - Krumke, Sven A1 - Megow, Nicole A1 - Rambau, Jörg A1 - Tuchscherer, Andreas A1 - Vredeveld, Tjark T1 - The Online Target Date Assignment Problem N2 - Many online problems encountered in real-life involve a two-stage decision process: upon arrival of a new request, an irrevocable first-stage decision (the assignment of a specific resource to the request) must be made immediately, while in a second stage process, certain ``subinstances'' (that is, the instances of all requests assigned to a particular resource) can be solved to optimality (offline) later. We introduce the novel concept of an \emph{Online Target Date Assignment Problem} (\textsc{OnlineTDAP}) as a general framework for online problems with this nature. Requests for the \textsc{OnlineTDAP} become known at certain dates. An online algorithm has to assign a target date to each request, specifying on which date the request should be processed (e.\,g., an appointment with a customer for a washing machine repair). The cost at a target date is given by the \emph{downstream cost}, the optimal cost of processing all requests at that date w.\,r.\,t.\ some fixed downstream offline optimization problem (e.\,g., the cost of an optimal dispatch for service technicians). We provide general competitive algorithms for the \textsc{OnlineTDAP} independently of the particular downstream problem, when the overall objective is to minimize either the sum or the maximum of all downstream costs. As the first basic examples, we analyze the competitive ratios of our algorithms for the par ticular academic downstream problems of bin-packing, nonpreemptive scheduling on identical parallel machines, and routing a traveling salesman. T3 - ZIB-Report - 05-61 KW - Online Algorithms KW - Online Target Date Assignment Problem Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-8945 ER - TY - THES A1 - Rambau, Jörg T1 - Polyhedral Subdivisions and Projections of Polytopes N2 - The present dissertation deals with the structure of polyhedral subdivisions of point configurations. Of particular interest are the global properties of the set of all subdivisions of a given point configuration. An important open problem in this context is the following: can one always transform any triangulation of a given point configuration to any other triangulation of the same configuration by means of bistellar operations? In other words, is the set of all triangulations of a given point configuration always bistellarly connected? The results presented in this thesis contribute progress from two directions. \begin{itemize} \item The set of all subdivisions that are induced by a polytope projection is in general not bistellarly connected in a generalized sense. This result is obtained by constructing a counterexample to the so-called Generalized Baues Conjecture.'' \item The set of all triangulations of a cyclic polytope forms a bounded poset. The covering relations are given by increasing bistellar operations. Thus we get an affirmative answer to the above question in the case of cyclic polytopes. \end{itemize} In the introduction, the mathematical environment of the structures under consideration is illuminated. The "Generalized Baues Conjecture" has connections to various mathematical concepts, such as combinatorial models for loop spaces, discriminants of polynomials in several variables, etc. The triangulation posets of cyclic polytopes are natural generalizations of the well-studied Tamari lattices in order theory. Moreover, there is a connection to the higher Bruhat orders, which have similar structural properties. As a by-product, the investigations yield the shellability of all triangulations of cyclic polytopes without new vertices. This is in particular interesting because most triangulations of cyclic polytopes are non-regular. N2 - Die vorliegende Dissertation beschäftigt sich mit strukturellen Fragen in der Theorie der polyedrischen Unterteilungen von Punktkonfigurationen. Hierbei sind vor allem globale Eigenschaften der Menge aller Unterteilungen einer gegebenen Punktkonfiguration von Interesse. Eine wichtige ungelöste Frage in diesem Zusammenhang ist die folgende: Ist es immer möglich, von einer beliebigen Triangulierung einer gegebenen Punktkonfiguration zu jeder anderen Triangulierung derselben Konfiguration zu gelangen, indem man sogenannte bistellare Operationen durchführt? Mit anderen Worten, ist die Menge aller Triangulierungen einer gegebenen Punktkonfiguration stets bistellar zusammenhängend? Die Ergebnisse der vorliegenden Doktorarbeit liefern auf zwei Seiten dieser nach wie vor offenen Frage Fortschritte: \begin{itemize} \item Die Menge aller durch eine Polytopprojektion induzierten Unterteilungen ist nicht immer --- in einem verallgemeinerten Sinne --- bistellar zusammenhängend. Dieses Resultat wird durch ein Gegenbeispiel zur sogenannten "Verallgemeinerten Baues Vermutung"' erzielt. \item Die Menge aller Triangulierungen eines zyklischen Polytops bildet eine beschränkte Halbordnung. Die Ueberdeckungsrelationen sind gerichtete bistellare Operationen. Für zyklische Polytope ist die obige Frage nach bistellarem Zusammenhang also positiv beantwortet. \end{itemize} In der Einleitung wird das mathematische Umfeld der betrachteten Strukturen näher beleuchtet: Die "Verallgemeinerte Baues Vermutung" steht in Verbindung mit verschiedensten mathematischen Konzepten, angefangen von kombinatorischen Modellen von Schleifenräumen bis hin zu Diskriminanten von Polynomen in mehreren Variablen. Die Triangulierungs-Halbordnungen von zyklischen Polytopen sind zugleich natürliche Verallgemeinerungen der gut studierten Tamari-Verbände in der Ordnungstheorie. Ausserdem existiert ein Zusammenhang mit den höheren Bruhat-Ordnungen, die ähnliche Struktureigenschaften aufweisen. Ein Nebenprodukt der Untersuchungen ist die Schälbarkeit aller Triangulierungen von zyklischen Polytopen ohne neue Ecken. Das ist um so interessanter, da die meisten Triangulierungen von zyklischen Polytopen nicht-regulär sind. KW - polyedrische Unterteilung KW - Triangulierung KW - Verallgemeinertes Baues-Problem KW - Zyklisches Polytop KW - Höhere Bruhat-Ordnung KW - polyhedral subdivision KW - triangulation KW - Generalized Baues Problem KW - cyclic polytope KW - higher Bruhat order Y1 - 1996 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-10271 SN - 3-8265-1955-8 ER - TY - GEN A1 - Grötschel, Martin A1 - Krumke, Sven A1 - Rambau, Jörg T1 - Wo bleibt der Aufzug? N2 - Dieser Artikel gibt eine allgemeinverständliche Einführung in die spezielle Problematik kombinatorischer Online-Problem am Beispiel der Fahrstuhlsteuerung. T3 - ZIB-Report - SC-99-29 KW - Aufzugsteuerung KW - Online-Optimierung KW - Echtzeit-Optimierung KW - kompetitive Analyse Y1 - 1999 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-4175 ER - TY - GEN A1 - Hauptmeier, Dietrich A1 - Krumke, Sven A1 - Rambau, Jörg A1 - Wirth., Hans-Christoph T1 - Euler is Standing in Line N2 - In this paper we study algorithms for ``Dial-a-Ride'' transportation problems. In the basic version of the problem we are given transportation jobs between the vertices of a graph and the goal is to find a shortest transportation that serves all the jobs. This problem is known to be NP-hard even on trees. We consider the extension when precedence relations between the jobs with the same source are given. Our results include a polynomial time algorithm on paths and an approximation algorithm on general graphs with a performance of~$9/4$. For trees we improve the performance to~$5/3$. T3 - ZIB-Report - SC-99-06 KW - NP-completeness KW - polynomial-time approximation algorithms KW - stacker-crane problem KW - vehicle routing KW - elevator system KW - Eulerian Cycle Y1 - 1999 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-3947 ER -