TY - GEN A1 - Löffler, Sven A1 - Becker, Ilja A1 - Hofstedt, Petra T1 - Enhancing constraint optimization problems with greedy search and clustering: a focus on the traveling salesman problem T2 - Proceedings of the 16th International Conference on Agents and Artificial Intelligence - Volume 3: ICAART Y1 - 2024 SN - 978-989-758-680-4 U6 - https://doi.org/10.5220/0012453000003636 SN - 2184-433X SP - 1170 EP - 1178 PB - SCITEPRESS - Science and Technology Publications ER - TY - GEN A1 - Löffler, Sven A1 - Hofstedt, Petra T1 - A constraint-based greedy-local-global search for the warehouse location problem T2 - IFIP Advances in Information and Communication Technology Y1 - 2024 SN - 9783031632181 U6 - https://doi.org/10.1007/978-3-031-63219-8_22 SN - 1868-4238 SP - 291 EP - 304 PB - Springer Nature Switzerland CY - Cham ER - TY - GEN A1 - Frank, Florian A1 - Buckel, Peter A1 - Hoegner, Ludwig A1 - Hofstedt, Petra T1 - A landmark selection method for object-based visual outdoor localization approaches of automated ground vehicles T2 - ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences N2 - Autonomous vehicles must navigate independently in an outdoor environment using features or objects. However, some objects may be more or less suitable for localization due to their attributes. Therefore, this work investigates the suitability of landmarks for camera- and object-based outdoor localization methods. First, object attributes are methodically derived from the requirements of object-based localization. The physical representation on the camera image plane, probability of occurrence, and persistence were identified as influencing the object localization suitability. The influence of the object’s camera image plane representation regarding object recognition algorithms is not considered or discussed, but advice on the minimum object pixel size is provided. The first milestone was the creation of an equation for object localization suitability calculation by normalizing and multiplying the identified attributes. Simultaneously, potential objects from the outdoor environment were identified, resulting in a structured object catalog. The results of the equation and catalog are a ranked according to the object localization suitability in a comparison table. Our comparison demonstrates that objects such as buildings or trees are more suitable than street lane markings for self-localization. However, most current datasets do not include the proposed instantiated objects. The paper addresses this issue, assists in the object selection for outdoor localization methods and provides input for the creation of future-oriented datasets and autonomous driving maps. Y1 - 2024 U6 - https://doi.org/10.5194/isprs-annals-X-4-W5-2024-163-2024 SN - 2194-9050 SP - 163 EP - 169 PB - Copernicus GmbH ER - TY - GEN A1 - Becker, Ilja A1 - Löffler, Sven A1 - Hofstedt, Petra ED - Machado, Jose Manuel F. ED - Chamoso, Pablo ED - Hernandez, Guillermo ED - Bocewicz, Grzegorz ED - Loukanova, Roussanka ED - Jove, Esteban ED - del Rey, Angel Martin ED - Ricca, Michela T1 - ML-based Automation of Constraint Satisfaction Model Transformation and Solver Configuration T2 - Distributed Computing and Artificial Intelligence, Special Sessions - DCAI 2022, 19th International Conference KW - Constraint Programming KW - Machine Learning Y1 - 2022 SN - 978-3-031-23209-1 SN - 978-3-031-23210-7 SP - 177 EP - 183 PB - Springer CY - Cham ER - TY - GEN A1 - Löffler, Sven A1 - Becker, Ilja A1 - Hofstedt, Petra ED - Strauss, Christine ED - Amagasa, Toshiyuki ED - Kotsis, Gabriele ED - Tjoa, A Min ED - Khalil, Ismail T1 - A Finite-Domain Constraint-Based Approach on the Stockyard Planning Problem T2 - Database and Expert Systems Applications : 34th International Conference, DEXA 2023, Penang, Malaysia, August 28–30, 2023, Proceedings, Part II Y1 - 2023 SN - 978-3-031-39820-9 SN - 978-3-031-39821-6 SP - 126 EP - 133 PB - Springer CY - Cham ER - TY - GEN A1 - Bels, Maximilian A1 - Löffler, Sven A1 - Becker, Ilja A1 - Hofstedt, Petra ED - Rocha, Ana Paula ED - Steels, Luc ED - van den Herik, H. Jaap T1 - Constraint-Based Filtering and Evaluation of CSP Search Trees T2 - Proceedings of the 15th International Conference on Agents and Artificial Intelligence - ICAART 2023, Volume 3 KW - Constraint Programming KW - Artificial Intelligence Y1 - 2023 SN - 978-989-758-623-1 U6 - https://doi.org/10.5220/0011641100003393 SP - 220 EP - 227 PB - Scitepress ER - TY - GEN A1 - Löffler, Sven A1 - Becker, Ilja A1 - Bückert, Carlo A1 - Hofstedt, Petra ED - Gini, Giuseppina ED - Nijmeijer, Henk ED - Filev, Dimitar T1 - Enhanced Optimal Beacon Placement for Indoor Positioning: A Set Variable Based Constraint Programming Approach T2 - Proceedings of the 20th International Conference on Informatics in Control, Automation and Robotics : November 13-15, 2023, in Rome, Italy, volume 1 KW - Beacon Placement KW - Constraint Programming KW - Decision Support Systems KW - Artificial Intelligence Y1 - 2023 SN - 978-989-758-670-5 U6 - https://doi.org/10.5220/0012203400003543 SP - 70 EP - 79 PB - Scitepress ER - TY - GEN A1 - Löffler, Sven A1 - Becker, Ilja A1 - Hofstedt, Petra A1 - Nitze, Andre A1 - Hennig, Silvia A1 - Klinge, Alexander ED - Klein, Maike ED - Krupka, Daniel ED - Winter, Cornelia ED - Wohlgemuth, Volker T1 - Planung des Ländlichen On-Demand-Verkehr - Probleme, Analyse und Algorithmen T2 - Informatik 2023 : Designing Futures - Zukünfte gestalten : 26.-29. September 2023, Berlin Y1 - 2023 SN - 978-3-88579-731-9 U6 - https://doi.org/10.18420/inf2023_177 SP - 1739 EP - 1750 PB - Gesellschaft für Informatik e.V. CY - Berlin ER - TY - GEN A1 - Pißarek, Adele A1 - Hofstedt, Petra A1 - Löffler, Sven ED - Dassisti, Michele ED - Madani, Kurosh ED - Panetto, Herve T1 - Stockyard Planning and Optimization Using Intelligent Search T2 - Innovative Intelligent Industrial Production and Logistics Y1 - 2025 SN - 978-3-031-80775-6 U6 - https://doi.org/10.1007/978-3-031-80775-6_7 SN - 1865-0937 VL - 2 SP - 94 EP - 110 PB - Springer Nature Switzerland CY - Cham ER - TY - CHAP A1 - Löffler, Sven A1 - Hofstedt, Petra ED - Nicosia, Guiseppe ED - Ojha, Varun ED - Giesselbach, Sven ED - Pardalos, M. Panos ED - Umeton, Renato T1 - A constraint-based savings algorithm for the Traveling Salesman Problem T2 - Machine Learning, Optimization and Data Science : 10th International Conference, LOD 2024, Castiglione Della Pescaia, Italy, September 22-25, 2024, Revised Selected Papers N2 - There exists a plethora of NP-hard problems for which obtaining an exact solution is computationally intensive while an approximate solution can be rapidly computed. The Traveling Salesman Problem (TSP) stands out as a prominent example within this problem class, being equally significant in both research and industry sectors. Exact methods for solving the TSP are typically infeasible within acceptable timeframes beyond a certain instance size. Due to the NP-hardness of the problem, computational time requirements would quickly escalate to weeks, months, years, or even millennia. In contrast, heuristic approaches often yield sufficiently good solutions rapidly, typically within seconds or minutes. However, the drawback lies in their tendency to produce only locally optimal solutions, which may deviate significantly from a global optimum. Nevertheless, heuristic methods remain preferred in industry due to their ability to find satisfactory solutions within reasonable timeframes. It is worth noting that even marginal improvements in solutions can translate into significant cost savings in practice. Hence, there is a demand for methods capable of swiftly providing high-quality solutions while also continuously searching for further, better solutions over time. This work aims to combine two approaches: heuristic search (utilizing two simple greedy algorithms and the savings algorithm developed by Clarke and Wright) and exact search (constraint programming), to solve TSPs. Using various TSP instances, we demonstrate that our approach yields a better solution than purely local methods in at least 80% of the cases. Furthermore, within the given time limit of 5 min, the new approach identifies a solution that is more than twice as good compared to traditional COP methods. KW - Constraints KW - Optimization KW - Traveling Salesman Problem Y1 - 2025 SN - 9783031824838 U6 - https://doi.org/10.1007/978-3-031-82484-5_15 SN - 0302-9743 VL - 2 SP - 203 EP - 217 PB - Springer Nature Switzerland CY - Cham ER - TY - CHAP A1 - Löffler, Sven A1 - Hofstedt, Petra ED - Rocha, Ana Paula ED - Steels, Luc ED - van den Herik, H. Jaap T1 - Greedy and local search-based constraint optimization of the travelling salesman problem T2 - Agents and Artificial Intelligence : 16th International Conference, ICAART 2024 Rome, Italy, February 24–26, 2024 : revised selected papers, Part II N2 - Constraint optimization problems offer a way to obtain a global solution for a given problem. However, the promise of finding a global solution often comes at the cost of significant time and computational resources. Greedy search, local search, and cluster identification methods represent alternative approaches, which can quickly lead to local optima. In our previous work presented at the 16th International Conference on Agents and Artificial Intelligence (ICAART) 2024 [19], we introduced new methods to combine constraint programming with greedy search and clustering methods in the context of the traveling salesman problem. In this paper, we explore the advantages of incorporating greedy search and local search, which can be seen as a clustering technique in this case, into constraint optimization methods without forsaking the pursuit of a global solution. The global search process is initially designed to behave similarly to a greedy search or local search. Compared to [19], we now considered more diverse greedy and iterated local search techniques as a new clustering method. Our approach aims to achieve two key objectives: first, to accelerate the process of finding of an initial solution, and second, to ensure that this solution possesses a high level of optimality. Our approach is an enhancement of the general branch-and-bound method in constraint programming. Finally, we validate our results using the traveling salesman problem as a case study. KW - Constraint Optimization KW - Informed and local search KW - Travelling Salesman Problem KW - TSP Y1 - 2025 SN - 9783031873294 U6 - https://doi.org/10.1007/978-3-031-87330-0_11 SN - 0302-9743 SP - 212 EP - 233 PB - Springer Nature Switzerland CY - Cham ER - TY - CHAP A1 - Assaf, George A1 - Löffler, Sven A1 - Hofstedt, Petra ED - Tack, Guido T1 - Optimized scheduling of medical appointment sequences using constraint programming T2 - Integration of constraint programming, artificial intelligence, and operations research : 22nd International Conference, CPAIOR 2025 Melbourne, VIC, Australia, November 10–13, 2025 : proceedings, Part I N2 - We propose a novel constraint-based model to efficiently tackle the medical appointment sequence scheduling problem (MASSP), inspired by a real-world problem at Charité – Universitätsmedizin Berlin. In many practical medical scenarios, scheduling a sequence of appointments, rather than a single appointment, has become increasingly essential for patients undergoing multi-stage treatments. The goal of the MASSP is to identify a set of medical resources with sufficient, consecutive, and available time slots in their calendars to create a sequence of appointments for effectively managing a treatment plan. The problem comprises various constraints, including the availability of both the intended patient and required medical resources, as well as the time and resource dependencies among the individual appointments that constitute the sequence. To address this, we formulate the problem as a constraint optimization problem () that not only captures the basic constraints of the MASSP but also optimizes resource assignment to ensure a fair workload distribution within the medical facility. The results of our experiments demonstrate that the model performs effectively under diverse conditions, which confirms the utility and robustness of the proposed model in optimizing resource allocation and ensuring equitable workload distribution. KW - Constraint Programming KW - Optimization KW - Medical Appointment Scheduling Y1 - 2025 SN - 978-3-031-95973-8 U6 - https://doi.org/10.1007/978-3-031-95973-8_1 SN - 0302-9743 SP - 1 EP - 16 PB - Springer Nature Switzerland CY - Cham ER - TY - GEN A1 - Löffler, Sven A1 - Abbenhaus, Viktoria A1 - Assaf, George A1 - Hofstedt, Petra ED - Gini, Giuseppina ED - Precup, Radu-Emil ED - Filev, Dimitar P. T1 - Solving the three-dimensional beacon placement problem using constraint-based methods, large neighborhood search, and evolutionary algorithms T2 - Proceedings of the 22nd International Conference on Informatics in Control, Automation and Robotics : Volume 1 : ICINCO N2 - With the increasing prevalence of large building complexes, indoor localization is becoming an area of growing significance. In critical situations, such as emergencies in factories or care facilities, the ability to locate a person quickly can be a matter of life and death. One possibility for localization are Bluetooth beacons, which are either attached to the person or in rooms. We pursue the latter approach, whereby the beacon signals are used to determine the position of a receiving device, e.g. a mobile phone. At this, the use of a sufficient number of beacons in the building must be ensured in order to guarantee adequate coverage. However, to minimize costs, it is equally important to avoid placing unnecessary beacons. This creates a challenging optimization problem that this paper addresses through three distinct approaches: constraint programming, large neighborhood search, and evolutionary algorithms. Using simulated three-dimensional buildings, we test and evaluate these m ethods, ultimately providing a practical and efficient approach applicable to real-world building environments. KW - Constraint Programming KW - AI Algorithms KW - Beacon Placement Y1 - 2025 SN - 978-989-758-770-2 U6 - https://doi.org/10.5220/0013724500003982 SP - 105 EP - 116 PB - SciTePress - Science and Technology Publications CY - Setúbal, Portugal ER - TY - GEN A1 - Assaf, George A1 - Löffler, Sven A1 - Hofstedt, Petra ED - Rocha, Ana Paula ED - Steels, Luc ED - van den Herik, H. Jaap T1 - Constraint-based optimization for scheduling medical appointments T2 - Proceedings of the 17th International Conference on Agents and Artificial Intelligence : volume 3: ICAART, 94-103, 2025 , Porto, Portugal N2 - In this paper, we introduce a novel approach for solving as well as optimizing the medical appointment scheduling problem (MASP) using constraint programming. The MASP is a complex and critical task in health care management, directly impacting both patient care and operational efficiency. We formalize the MASP as a set of constraints that encode diverse requirements for scheduling medical appointments, including intuitive requirements such as the availability of both patients and medical resources, including physicians, nurses and medical equipment. Furthermore, our model accounts for patient preferences, such as favoring specific dates and/or particular resources whenever feasible. The proposed method incorporates optimization techniques that enhance the scheduling process by considering appointment urgency and balancing workload distribution among the assigned resources, thereby improving the allocation of medical resources. As an outcome, our constraint model demonstrates high ef ficiency by scheduling medical appointments in just milliseconds. KW - Constraint Programming KW - Optimization KW - Medical Appointment Scheduling Y1 - 2025 SN - 978-989-758-737-5 U6 - https://doi.org/10.5220/0013091300003890 SP - 94 EP - 103 PB - SciTePress - Science and Technology Publications CY - Setúbal, Portugal ER - TY - CHAP A1 - Löffler, Sven A1 - Hofstedt, Petra ED - Gini, Giuseppina ED - Nijmeijer, Henk ED - Filev, Dimitar T1 - Enhanced optimal beacon placement for indoor positioning : refining the search process T2 - Informatics in control, automation and robotics : 20th International Conference, ICINCO 2023, Rome, Italy, November 13–15, 2023 : revised selected papers N2 - Indoor localization plays a key role across diverse environments such as hospitals, retirement homes, and emergency response scenarios. Ensuring the efficient and precise tracking of mobile individuals indoors heavily relies on the strategic deployment of sensors. Manual placement of beacons (sensors) for indoor positioning within a building poses significant challenges and time constraints. Consequently, numerous researchers have explored this problem domain, employing diverse algorithms and addressing various practical scenarios. In our previous works at the ACS/IEEE International Conference on Computer Systems and Applications (AICCSA 2022) [20] and the 20th International Conference on Informatics in Control, Automation and Robotics (ICINCO 2023) [19], we introduced two novel approaches that leverage constraint programming with exclusively Boolean variables respectively only set variables and Boolean variables to efficiently place Bluetooth Low Energy (BLE) beacons in indoor scenarios. We evaluated the quality of our results by comparing them against manually optimized beacon placement and assessing their performance in four real-world school buildings. This paper extends the findings of [19, 20] by new approaches on the search in the constraint solving process using greedy search and local search techniques. KW - Constraint Programming KW - Search Methods KW - Beacon Placement Y1 - 2025 SN - 978-3-031-94989-0 U6 - https://doi.org/10.1007/978-3-031-94989-0_5 SN - 1876-1100 SP - 97 EP - 124 PB - Springer Nature Switzerland CY - Cham ER - TY - CHAP A1 - Löffler, Sven A1 - Abbenhaus, Viktoria A1 - Assaf, George A1 - Hofstedt, Petra ED - Braun, Tanya ED - Paaßen, Benjamin ED - Stolzenburg, Frieder T1 - A hybrid constraint-based, greedy, and local search approach for the transshipment problem T2 - KI 2025 : advances in artificial intelligence : 48th German Conference on AI, Potsdam, Germany, September 16–19, 2025 : proceedings N2 - The efficient resolution of logistics problems, particularly those aimed at minimizing costs and reducing environmental impact, represents a critical challenge in our globalized world. A prominent example of such problems is the Transshipment Problem, which seeks to determine the most cost-effective paths from sources (e.g., producers) through transshipment points to sinks (e.g., customers). Approaches to addressing this problem range from greedy algorithms, which may rapidly yield locally optimal solutions, to constraint-based methods that, given sufficient resources and computation time, can identify globally optimal solutions. In this study, we propose a hybrid approach that integrates greedy strategies into the solution process of constraint modeling for the Transshipment Problem. This integration aims to expedite the discovery of high-quality initial solutions while preserving the global optimization capabilities inherent in constraint-based search methods. To validate the effectiveness of this new hybrid approach, we conducted an extensive series of experiments, which demonstrate its significant advantages in solving the Transshipment Problem compared to both a conventional constraint model and pure greedy methods. KW - Constraint Programming KW - Search methods KW - Transshipment problem Y1 - 2025 SN - 978-3-032-02813-6 U6 - https://doi.org/10.1007/978-3-032-02813-6_7 SN - 0302-9743 SP - 91 EP - 103 PB - Springer Nature Switzerland CY - Cham ER - TY - GEN A1 - Assaf, George A1 - Löffler, Sven A1 - Hofstedt, Petra T1 - Parallel constraint satisfaction for optimizing medical appointment scheduling T2 - Proceedings of DECLARE 2025, Conference on Declarative Programming N2 - We explore the use of parallel constraint satisfaction to eciently solve the medical appointment scheduling problem (MASP). The medical appointment scheduling problem entails the coordination of suitable medical resources such as medical sta and equipment that share available time slots in their calendars to create an appointment for a patient seeking a specic medical service. The problem is subject to constraints as well as optimization criteria derived from treatment plans, medical protocols, and patient preferences. However, in large-scale healthcare settings, traditional constraint programming methods face signicant performance challenges (in terms of resolution time) due to the large number of resources within the medical facility as well as extended scheduling horizons. To overcome the performance limitations, we employ parallel portfolio search, which simultaneously utilizes multiple cores and diverse search strategies to eciently identify optimal solutions. The parallelized MASP demonstrates dramatic improvements over single-threaded constraint solving, signicantly reducing resolution times to clinically acceptable time frames for complex MASP instances, and increasing the overall solution quality. KW - Constraint Programming KW - Parallel Processing KW - Medical Appointment Scheduling Y1 - 2025 UR - https://drive.google.com/file/d/16XPXoY1StYm_YCwXrKf1ZE9G8meRBzsu/view UR - https://sites.google.com/uevora.pt/declare2025/home SP - 1 EP - 13 ER - TY - GEN A1 - Löffler, Sven A1 - Hofstedt, Petra T1 - An enhanced constraint-based approach for automating digital signal placement in railway digitalization T2 - SN Computer science N2 - The goal of digitalization is to standardize processes and reduce resource consumption. However, achieving this goal often requires substantial intellectual and resource-intensive investments. In this work we fokus on the automatic placement of digital signals at appropriate distances from existing switches along station tracks, replacing analog signals. In contrast to previous approaches, we extend the problem scope to better reflect real-world application scenarios by supporting multiple entry and exit tracks as well as bidirectional train movements. We formulate a constraint problem to define the problem and introduce methods to accelerate the solution process, making it scalable to large problem instances. The proposed approach is validated through a series of tests generated by our newly developed problem generator, illustrating its applicability to real-world challenges. KW - Constraint Programming KW - Railway Digitalization Y1 - 2025 U6 - https://doi.org/10.1007/s42979-025-04233-5 SN - 2661-8907 VL - 6 SP - 1 EP - 17 PB - Springer Singapore CY - Singapore ER -