These are the instance files used for all computations in the research paper "Exact approach... more These are the instance files used for all computations in the research paper "Exact approaches for the combined cell layout problem"
In this work, we introduce and analyze an extension of the Linear Ordering Problem ( LOP) . The L... more In this work, we introduce and analyze an extension of the Linear Ordering Problem ( LOP) . The LOP aims to find a simultaneous permutation of rows and columns of a given weight matrix such that the sum of the weights in the upper triangle is maximized. We propose the weighted Linear Ordering Problem ( wLOP) that additionally considers individual node weights.
Integration of Constraint Programming, Artificial Intelligence, and Operations Research
Attended Home Delivery (AHD) systems are used whenever a supplying company offers online shopping... more Attended Home Delivery (AHD) systems are used whenever a supplying company offers online shopping services that require that customers must be present when their deliveries arrive. Therefore, the supplying company and the customer must both agree on a time window, which ideally is rather short, during which delivery is guaranteed. Typically, a capacitated Vehicle Routing Problem with Time Windows forms the underlying optimization problem of the AHD system. In this work, we consider an AHD system that runs the online grocery shopping service of an international grocery retailer. The ordering phase, during which customers place their orders through the web service, is the computationally most challenging part of the AHD system. The delivery schedule must be built dynamically as new orders are placed. We propose a solution approach that allows to (non-stochastically) determine which delivery time windows can be offered to potential customers. We split the computations of the ordering phase into four key steps. For performing these basic steps we suggest both a heuristic approach and a hybrid approach employing mixed-integer linear programs. In an experimental evaluation we demonstrate the efficiency of our approaches.
Grocery home delivery services require customers to be present when their deliveries arrive. Henc... more Grocery home delivery services require customers to be present when their deliveries arrive. Hence, the grocery retailer and the customer must mutually agree on a time window during which the delivery can be guaranteed. This concept is referred to as the Attended Home Delivery (AHD) problem. The phase during which customers place orders, usually through a web service, constitutes the computationally most challenging part of the logistical processes behind such services. The system must determine potential delivery time windows that can be offered to incoming customers and incrementally build the delivery schedule as new orders are placed. Typically, a Vehicle Routing Problem with Time Windows forms the underlying optimization problem. This work is concerned with the use case given by an international grocery retailer’s online shopping service. We present an analysis of efficient solution methods that can be employed to AHD services. We provide several heuristic approaches for tackli...
2017 IEEE International Conference on Industrial Engineering and Engineering Management (IEEM)
We consider a new facility layout problem. The Directed Circular Facility Layout Problem (DCFLP) ... more We consider a new facility layout problem. The Directed Circular Facility Layout Problem (DCFLP) seeks to optimally arrange machines on a circular layout with given material flow direction. The DCFLP allows for a wide range of applications and contains several other relevant layout problems as special cases. We model the DCFLP as a Linear Ordering Problem and solve it using an Integer Linear Program and a Tabu Search heuristic. In our computational study we show that the DCFLP is easier to solve for both exact and heuristic approaches than other related layout problems.
2018 IEEE International Conference on Industrial Engineering and Engineering Management (IEEM)
The Combined Cell Layout Problem aims to minimize the material handling costs in a cellular manuf... more The Combined Cell Layout Problem aims to minimize the material handling costs in a cellular manufacturing system with at least two cells where processing occurs, and in the presence of pieces that need to be processed in more than one cell. The alignment of the machines in each cell can follow a row or a circular layout. We propose an Integer Linear Programming approach for solving this problem. In a computational study we show that our approach is able to solve instances with up to 240 machines arranged in 10 cells to optimality within one minute.
Attended Home Delivery systems are used whenever a retailing company offers online shopping servi... more Attended Home Delivery systems are used whenever a retailing company offers online shopping services that require customers to be present when their deliveries arrive. Therefore, the retail company and the customer must mutually agree on a time window during which the delivery can be assured. When placing a new order, the customer receives a selection of available delivery time slots depending on the delivery location and already accepted orders. Then, the customer selects his/her preferred delivery time slot and the order is scheduled. In general, the larger the selection, the more likely the customer finds a suitable delivery time slot. We denote the problem of determining the maximal number of feasible delivery time slots for a potential new order as the Slot Optimization Problem (SOP). It is common practice to hide certain delivery options from the customer or offer them at different rates in order to steer the incoming demand such that the expected profit is maximized. In any c...
The capacitated Vehicle Routing Problem with structured Time Windows (cVRPsTW) is concerned with ... more The capacitated Vehicle Routing Problem with structured Time Windows (cVRPsTW) is concerned with finding optimal tours for vehicles with given capacity constraints to deliver goods to customers within assigned time windows that can hold several customers and have a special structure (in our case equidistant and non-overlapping). In this work, we consider an on-line variant of the cVRPsTW that arises in the online shopping service of an international supermarket chain: customers choose a delivery time window for their order online, and the fleet’s tours are updated accordingly in real time. This leads to two challenges. First, the new customers need to be inserted at a suitable place in one of the existing tours. Second, the new customers have to be inserted in real time due to very high request rates. This is why we apply a computationally cheap, two-step approach consisting of an insertion step and an improvement step. In this context, we present a Mixed-Integer Linear Program (MIL...
In this paper we consider the Combined Cell Layout Problem (CCLP), the Multi-Bay Facility Layout ... more In this paper we consider the Combined Cell Layout Problem (CCLP), the Multi-Bay Facility Layout Problem (MBFLP) and several generalizations of the MBFLP, which have wide applications, e.g., in factory planning, heavy manufacturing, semiconductor fabrication and arranging rooms in hospitals. Given a set of cells of type single-row or directed-circular and a set of one-dimensional departments with pairwise transport weights between them, the CCLP asks for an assignment of the departments to the cells such that departments in the same cell do not overlap and such that the sum of the weighted center-to-center distances is minimized. Distances between departments in the same cell are measured according to the layout type of the cell and otherwise their distance equals the sum of the distances to the associated (un-) loading stations of the cells plus possible space between the cells. We solve the CCLP exactly by enumerating over all assignments of the departments to the cells and solvin...
The university course timetabling problem deals with the task of scheduling lectures of a set of ... more The university course timetabling problem deals with the task of scheduling lectures of a set of university courses into a given number of rooms and time periods, taking into account various hard and soft constraints. The goal of the International Timetabling Competitions ITC2002 and ITC2007 was to establish models for comparison that cover the most frequently found use cases. Our model, motivated by a project with University College London (UCL), builds on the standard model from track 3 of ITC2007. Compared to the standard model from the literature, we cover several new constraints and extra features. For example, we expand the ITC2007 framework to generate a timetable for several weeks of the term instead of only one and introduce the corresponding timetable regularity metric, which measures the consistency of time and room assignments for a course throughout the term. We suggest an Integer Linear Programming approach for solving this expanded timetabling problem and introduce a ...
The Dial-a-Ride Problem (DARP) aims to find a set of minimal cost tours for passenger vehicles in... more The Dial-a-Ride Problem (DARP) aims to find a set of minimal cost tours for passenger vehicles in order to satisfy a set of transport requests. Each request requires to pickup one or more passengers at a defined pickup point and then drop-off the passengers at the desired destination. In this work, we consider a DARP that has been implemented by an Austrian mobility provider. The company focuses on rural regions that suffer from insufficient public transportation and offers a sustainable form of mobility. Moreover, the provider is especially interested in improving the sharing rates of the mobility service. Therefore, we propose a Large Neighborhood Search for solving the respective DARP. In a computational study, we compare different configurations of the service and identify the most promising configurations regarding sharing rates, passenger convenience and, hence, overall efficiency of the service.
We discuss a new facility layout problem, the so-called Directed Circular Facility Layout Problem... more We discuss a new facility layout problem, the so-called Directed Circular Facility Layout Problem . The aims to find an optimal arrangement of machines on a circular material handling system such that the total weighted sum of the center-to-center distances between all pairs of machines measured in clockwise direction is minimized. Several real-world applications, like for example the optimal arrangement of a set of cutting tools on a tool turret, can be modeled as a . Further, the generalizes a couple of layout problems that are well-discussed in literature. We show that the can be modeled as a Linear Ordering Problem . Hence, it can be solved efficiently by using exact and heuristic approaches for the . First, we apply a Semidefinite Programming as well as an Integer Linear Programming approach. Moreover, we use a Tabu Search and a Variable Neighborhood Search heuristic, for solving the . Finally, we compare the practical performance of our approaches in a computational study.
These are the instance files used for all computations in the research paper "Exact approach... more These are the instance files used for all computations in the research paper "Exact approaches for the combined cell layout problem"
In this work, we introduce and analyze an extension of the Linear Ordering Problem ( LOP) . The L... more In this work, we introduce and analyze an extension of the Linear Ordering Problem ( LOP) . The LOP aims to find a simultaneous permutation of rows and columns of a given weight matrix such that the sum of the weights in the upper triangle is maximized. We propose the weighted Linear Ordering Problem ( wLOP) that additionally considers individual node weights.
Integration of Constraint Programming, Artificial Intelligence, and Operations Research
Attended Home Delivery (AHD) systems are used whenever a supplying company offers online shopping... more Attended Home Delivery (AHD) systems are used whenever a supplying company offers online shopping services that require that customers must be present when their deliveries arrive. Therefore, the supplying company and the customer must both agree on a time window, which ideally is rather short, during which delivery is guaranteed. Typically, a capacitated Vehicle Routing Problem with Time Windows forms the underlying optimization problem of the AHD system. In this work, we consider an AHD system that runs the online grocery shopping service of an international grocery retailer. The ordering phase, during which customers place their orders through the web service, is the computationally most challenging part of the AHD system. The delivery schedule must be built dynamically as new orders are placed. We propose a solution approach that allows to (non-stochastically) determine which delivery time windows can be offered to potential customers. We split the computations of the ordering phase into four key steps. For performing these basic steps we suggest both a heuristic approach and a hybrid approach employing mixed-integer linear programs. In an experimental evaluation we demonstrate the efficiency of our approaches.
Grocery home delivery services require customers to be present when their deliveries arrive. Henc... more Grocery home delivery services require customers to be present when their deliveries arrive. Hence, the grocery retailer and the customer must mutually agree on a time window during which the delivery can be guaranteed. This concept is referred to as the Attended Home Delivery (AHD) problem. The phase during which customers place orders, usually through a web service, constitutes the computationally most challenging part of the logistical processes behind such services. The system must determine potential delivery time windows that can be offered to incoming customers and incrementally build the delivery schedule as new orders are placed. Typically, a Vehicle Routing Problem with Time Windows forms the underlying optimization problem. This work is concerned with the use case given by an international grocery retailer’s online shopping service. We present an analysis of efficient solution methods that can be employed to AHD services. We provide several heuristic approaches for tackli...
2017 IEEE International Conference on Industrial Engineering and Engineering Management (IEEM)
We consider a new facility layout problem. The Directed Circular Facility Layout Problem (DCFLP) ... more We consider a new facility layout problem. The Directed Circular Facility Layout Problem (DCFLP) seeks to optimally arrange machines on a circular layout with given material flow direction. The DCFLP allows for a wide range of applications and contains several other relevant layout problems as special cases. We model the DCFLP as a Linear Ordering Problem and solve it using an Integer Linear Program and a Tabu Search heuristic. In our computational study we show that the DCFLP is easier to solve for both exact and heuristic approaches than other related layout problems.
2018 IEEE International Conference on Industrial Engineering and Engineering Management (IEEM)
The Combined Cell Layout Problem aims to minimize the material handling costs in a cellular manuf... more The Combined Cell Layout Problem aims to minimize the material handling costs in a cellular manufacturing system with at least two cells where processing occurs, and in the presence of pieces that need to be processed in more than one cell. The alignment of the machines in each cell can follow a row or a circular layout. We propose an Integer Linear Programming approach for solving this problem. In a computational study we show that our approach is able to solve instances with up to 240 machines arranged in 10 cells to optimality within one minute.
Attended Home Delivery systems are used whenever a retailing company offers online shopping servi... more Attended Home Delivery systems are used whenever a retailing company offers online shopping services that require customers to be present when their deliveries arrive. Therefore, the retail company and the customer must mutually agree on a time window during which the delivery can be assured. When placing a new order, the customer receives a selection of available delivery time slots depending on the delivery location and already accepted orders. Then, the customer selects his/her preferred delivery time slot and the order is scheduled. In general, the larger the selection, the more likely the customer finds a suitable delivery time slot. We denote the problem of determining the maximal number of feasible delivery time slots for a potential new order as the Slot Optimization Problem (SOP). It is common practice to hide certain delivery options from the customer or offer them at different rates in order to steer the incoming demand such that the expected profit is maximized. In any c...
The capacitated Vehicle Routing Problem with structured Time Windows (cVRPsTW) is concerned with ... more The capacitated Vehicle Routing Problem with structured Time Windows (cVRPsTW) is concerned with finding optimal tours for vehicles with given capacity constraints to deliver goods to customers within assigned time windows that can hold several customers and have a special structure (in our case equidistant and non-overlapping). In this work, we consider an on-line variant of the cVRPsTW that arises in the online shopping service of an international supermarket chain: customers choose a delivery time window for their order online, and the fleet’s tours are updated accordingly in real time. This leads to two challenges. First, the new customers need to be inserted at a suitable place in one of the existing tours. Second, the new customers have to be inserted in real time due to very high request rates. This is why we apply a computationally cheap, two-step approach consisting of an insertion step and an improvement step. In this context, we present a Mixed-Integer Linear Program (MIL...
In this paper we consider the Combined Cell Layout Problem (CCLP), the Multi-Bay Facility Layout ... more In this paper we consider the Combined Cell Layout Problem (CCLP), the Multi-Bay Facility Layout Problem (MBFLP) and several generalizations of the MBFLP, which have wide applications, e.g., in factory planning, heavy manufacturing, semiconductor fabrication and arranging rooms in hospitals. Given a set of cells of type single-row or directed-circular and a set of one-dimensional departments with pairwise transport weights between them, the CCLP asks for an assignment of the departments to the cells such that departments in the same cell do not overlap and such that the sum of the weighted center-to-center distances is minimized. Distances between departments in the same cell are measured according to the layout type of the cell and otherwise their distance equals the sum of the distances to the associated (un-) loading stations of the cells plus possible space between the cells. We solve the CCLP exactly by enumerating over all assignments of the departments to the cells and solvin...
The university course timetabling problem deals with the task of scheduling lectures of a set of ... more The university course timetabling problem deals with the task of scheduling lectures of a set of university courses into a given number of rooms and time periods, taking into account various hard and soft constraints. The goal of the International Timetabling Competitions ITC2002 and ITC2007 was to establish models for comparison that cover the most frequently found use cases. Our model, motivated by a project with University College London (UCL), builds on the standard model from track 3 of ITC2007. Compared to the standard model from the literature, we cover several new constraints and extra features. For example, we expand the ITC2007 framework to generate a timetable for several weeks of the term instead of only one and introduce the corresponding timetable regularity metric, which measures the consistency of time and room assignments for a course throughout the term. We suggest an Integer Linear Programming approach for solving this expanded timetabling problem and introduce a ...
The Dial-a-Ride Problem (DARP) aims to find a set of minimal cost tours for passenger vehicles in... more The Dial-a-Ride Problem (DARP) aims to find a set of minimal cost tours for passenger vehicles in order to satisfy a set of transport requests. Each request requires to pickup one or more passengers at a defined pickup point and then drop-off the passengers at the desired destination. In this work, we consider a DARP that has been implemented by an Austrian mobility provider. The company focuses on rural regions that suffer from insufficient public transportation and offers a sustainable form of mobility. Moreover, the provider is especially interested in improving the sharing rates of the mobility service. Therefore, we propose a Large Neighborhood Search for solving the respective DARP. In a computational study, we compare different configurations of the service and identify the most promising configurations regarding sharing rates, passenger convenience and, hence, overall efficiency of the service.
We discuss a new facility layout problem, the so-called Directed Circular Facility Layout Problem... more We discuss a new facility layout problem, the so-called Directed Circular Facility Layout Problem . The aims to find an optimal arrangement of machines on a circular material handling system such that the total weighted sum of the center-to-center distances between all pairs of machines measured in clockwise direction is minimized. Several real-world applications, like for example the optimal arrangement of a set of cutting tools on a tool turret, can be modeled as a . Further, the generalizes a couple of layout problems that are well-discussed in literature. We show that the can be modeled as a Linear Ordering Problem . Hence, it can be solved efficiently by using exact and heuristic approaches for the . First, we apply a Semidefinite Programming as well as an Integer Linear Programming approach. Moreover, we use a Tabu Search and a Variable Neighborhood Search heuristic, for solving the . Finally, we compare the practical performance of our approaches in a computational study.
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Papers by Kerstin Maier