We study the problem of reconstructing (0, 1)-matrices based on projections along a small number ... more We study the problem of reconstructing (0, 1)-matrices based on projections along a small number of directions. This discrete inverse problem is generally hard to solve for more than 3 projection directions. Building on previous work by the authors, we give a problem formulation with the objective of finding matrices with the maximal number of neighboring ones. A solution approach based on variable splitting and the use of subgradient optimization is given. Further, computational results are given for some structured instances. Optimal solutions are found for instances with up to 10,000 binary variables.
This paper considers a maritime inventory routing problem faced by a major cement producer. A het... more This paper considers a maritime inventory routing problem faced by a major cement producer. A heterogeneous fleet of bulk ships transport multiple non-mixable cement products from producing factories to regional silo stations along the coast of Norway. Inventory constraints are present both at the factories and the silos, and there are upper and lower limits for all inventories. The ship fleet capacity is limited, and in peak periods the demand for cement products at the silos exceeds the fleet capacity. In addition, constraints regarding the capacity of the ships' cargo holds, the depth of the ports and the fact that different cement products cannot be mixed must be taken into consideration. A construction heuristic embedded in a genetic algorithmic framework is developed. The approach adopted is used to solve real instances of the problem within reasonable solution time and with good quality solutions.
... For a focused literature survey, we refer to Flatberg et al. ... the solver must support lock... more ... For a focused literature survey, we refer to Flatberg et al. ... the solver must support locking parts of the current plan that should not be modified during further optimization. ... The inherent complexity of these problems has led us to choose a unified meta-heuristic approach in SPIDER ...
There is a strong pressure on economy in the distribution of media products. Two important remedi... more There is a strong pressure on economy in the distribution of media products. Two important remedies are more efficient carrier routes and distribution of side products. Both call for effective and dynamic route design and revision processes. These processes are complex, time-consuming, and costly. The size of industrial carrier route planning instances may cause performance problems for VRP algorithms. In the VRP literature, the Capacitated Arc Routing Problem (CARP) is often advocated as an adequate model for applications such as newspaper delivery and garbage collection. We argue that a better model is the Node Edge Arc Routing Problem (NEARP). We describe how we have extended a VRP solver to enable modeling of the NEARP, and extended it with a framework for multi-level aggregation of demand. An aggregation heuristic that is based on the underlying road topology is presented. The resulting solver has been integrated in a commercial web based system for route management and tested by pilot users. We present experimental results on real-life data from newspaper distribution. Results on standard CARP and NEARP instances from the literature are given, including several new best known solutions.
Dynamic and stochastic vehicle routing problems are receiving more attention as both algorithms a... more Dynamic and stochastic vehicle routing problems are receiving more attention as both algorithms and computing technology advances. The dynamic aspects are important in many applications and research on practical algorithms is an area with increasing activity. We present a framework for representing dynamic and stochastic vehicle routing problems. The framework is intended for use in creating and running benchmark tests.
... AUTHOR(S) Truls Flatberg, Geir Hasle, Oddvar Kloster, Eivind J. Nilssen, and Atle Riise CLIEN... more ... AUTHOR(S) Truls Flatberg, Geir Hasle, Oddvar Kloster, Eivind J. Nilssen, and Atle Riise CLIENT(S) ... Examples are time dependent travel times in the road network (eg rush hour congestions), and time dependent probabilities for occurrence of new transport requests in a ...
We study the problem of reconstructing (0, 1)-matrices based on projections along a small number ... more We study the problem of reconstructing (0, 1)-matrices based on projections along a small number of directions. This discrete inverse problem is generally hard to solve for more than 3 projection directions. Building on previous work by the authors, we give a problem formulation with the objective of finding matrices with the maximal number of neighboring ones. A solution approach based on variable splitting and the use of subgradient optimization is given. Further, computational results are given for some structured instances. Optimal solutions are found for instances with up to 10,000 binary variables.
This paper considers a maritime inventory routing problem faced by a major cement producer. A het... more This paper considers a maritime inventory routing problem faced by a major cement producer. A heterogeneous fleet of bulk ships transport multiple non-mixable cement products from producing factories to regional silo stations along the coast of Norway. Inventory constraints are present both at the factories and the silos, and there are upper and lower limits for all inventories. The ship fleet capacity is limited, and in peak periods the demand for cement products at the silos exceeds the fleet capacity. In addition, constraints regarding the capacity of the ships' cargo holds, the depth of the ports and the fact that different cement products cannot be mixed must be taken into consideration. A construction heuristic embedded in a genetic algorithmic framework is developed. The approach adopted is used to solve real instances of the problem within reasonable solution time and with good quality solutions.
... For a focused literature survey, we refer to Flatberg et al. ... the solver must support lock... more ... For a focused literature survey, we refer to Flatberg et al. ... the solver must support locking parts of the current plan that should not be modified during further optimization. ... The inherent complexity of these problems has led us to choose a unified meta-heuristic approach in SPIDER ...
There is a strong pressure on economy in the distribution of media products. Two important remedi... more There is a strong pressure on economy in the distribution of media products. Two important remedies are more efficient carrier routes and distribution of side products. Both call for effective and dynamic route design and revision processes. These processes are complex, time-consuming, and costly. The size of industrial carrier route planning instances may cause performance problems for VRP algorithms. In the VRP literature, the Capacitated Arc Routing Problem (CARP) is often advocated as an adequate model for applications such as newspaper delivery and garbage collection. We argue that a better model is the Node Edge Arc Routing Problem (NEARP). We describe how we have extended a VRP solver to enable modeling of the NEARP, and extended it with a framework for multi-level aggregation of demand. An aggregation heuristic that is based on the underlying road topology is presented. The resulting solver has been integrated in a commercial web based system for route management and tested by pilot users. We present experimental results on real-life data from newspaper distribution. Results on standard CARP and NEARP instances from the literature are given, including several new best known solutions.
Dynamic and stochastic vehicle routing problems are receiving more attention as both algorithms a... more Dynamic and stochastic vehicle routing problems are receiving more attention as both algorithms and computing technology advances. The dynamic aspects are important in many applications and research on practical algorithms is an area with increasing activity. We present a framework for representing dynamic and stochastic vehicle routing problems. The framework is intended for use in creating and running benchmark tests.
... AUTHOR(S) Truls Flatberg, Geir Hasle, Oddvar Kloster, Eivind J. Nilssen, and Atle Riise CLIEN... more ... AUTHOR(S) Truls Flatberg, Geir Hasle, Oddvar Kloster, Eivind J. Nilssen, and Atle Riise CLIENT(S) ... Examples are time dependent travel times in the road network (eg rush hour congestions), and time dependent probabilities for occurrence of new transport requests in a ...
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Papers by T. Flatberg