170 research outputs found
Dynamic approach to solve the daily drayage problem with travel time uncertainty
The intermodal transport chain can become more e cient by means of a good organization of
drayage movements. Drayage in intermodal container terminals involves the pick up and delivery
of containers at customer locations, and the main objective is normally the assignment
of transportation tasks to the di erent vehicles, often with the presence of time windows. This
scheduling has traditionally been done once a day and, under these conditions, any unexpected
event could cause timetable delays. We propose to use the real-time knowledge about vehicle
position to solve this problem, which permanently allows the planner to reassign tasks in case
the problem conditions change. This exact knowledge of the position of the vehicles is possible
using a geographic positioning system by satellite (GPS, Galileo, Glonass), and the results show
that this additional data can be used to dynamically improve the solution
A Parallel Monte-Carlo Tree Search-Based Metaheuristic For Optimal Fleet Composition Considering Vehicle Routing Using Branch & Bound
In this paper, a Monte-Carlo Tree Search (MCTS)-based metaheuristic is
developed that guides a Branch & Bound (B&B) algorithm to find the globally
optimal solution to the heterogeneous fleet composition problem while
considering vehicle routing. Fleet Size and Mix Vehicle Routing Problem with
Time Windows (FSMVRPTW). The metaheuristic and exact algorithms are implemented
in a parallel hybrid optimization algorithm where the metaheuristic rapidly
finds feasible solutions that provide candidate upper bounds for the B&B
algorithm which runs simultaneously. The MCTS additionally provides a candidate
fleet composition to initiate the B&B search. Experiments show that the
proposed approach results in significant improvements in computation time and
convergence to the optimal solution.Comment: Submitted to the IEEE Intelligent Vehicles Symposium 202
Pricing routines for vehicle routing with time windows on road networks
Several very effective exact algorithms have been developed for vehicle routing problems with time windows. Unfortunately, most of these algorithms cannot be applied to instances that are defined on road networks, because they implicitly assume that the cheapest path between two customers is equal to the quickest path. Garaix and coauthors proposed to tackle this issue by first storing alternative paths in an auxiliary multi-graph, and then using that multi-graph within a branch-and-price algorithm. We show that, if one works with the original road network rather than the multi-graph, then one can solve the pricing subproblem more quickly, in both theory and practice
Pricing routines for vehicle routing with time windows on road networks
Several very effective exact algorithms have been developed for vehicle routing problems with time windows. Unfortunately, most of these algorithms cannot be applied to instances that are defined on road networks, because they implicitly assume that the cheapest path between two customers is equal to the quickest path. Garaix and coauthors proposed to tackle this issue by first storing alternative paths in an auxiliary multi-graph, and then using that multi-graph within a branch-and-price algorithm. We show that, if one works with the original road network rather than the multi-graph, then one can solve the pricing subproblem more quickly, in both theory and practice
Deep Policy Dynamic Programming for Vehicle Routing Problems
Routing problems are a class of combinatorial problems with many practical
applications. Recently, end-to-end deep learning methods have been proposed to
learn approximate solution heuristics for such problems. In contrast, classical
dynamic programming (DP) algorithms guarantee optimal solutions, but scale
badly with the problem size. We propose Deep Policy Dynamic Programming (DPDP),
which aims to combine the strengths of learned neural heuristics with those of
DP algorithms. DPDP prioritizes and restricts the DP state space using a policy
derived from a deep neural network, which is trained to predict edges from
example solutions. We evaluate our framework on the travelling salesman problem
(TSP), the vehicle routing problem (VRP) and TSP with time windows (TSPTW) and
show that the neural policy improves the performance of (restricted) DP
algorithms, making them competitive to strong alternatives such as LKH, while
also outperforming most other 'neural approaches' for solving TSPs, VRPs and
TSPTWs with 100 nodes.Comment: 21 page
Combining Reinforcement Learning and Constraint Programming for Combinatorial Optimization
Combinatorial optimization has found applications in numerous fields, from
aerospace to transportation planning and economics. The goal is to find an
optimal solution among a finite set of possibilities. The well-known challenge
one faces with combinatorial optimization is the state-space explosion problem:
the number of possibilities grows exponentially with the problem size, which
makes solving intractable for large problems. In the last years, deep
reinforcement learning (DRL) has shown its promise for designing good
heuristics dedicated to solve NP-hard combinatorial optimization problems.
However, current approaches have two shortcomings: (1) they mainly focus on the
standard travelling salesman problem and they cannot be easily extended to
other problems, and (2) they only provide an approximate solution with no
systematic ways to improve it or to prove optimality. In another context,
constraint programming (CP) is a generic tool to solve combinatorial
optimization problems. Based on a complete search procedure, it will always
find the optimal solution if we allow an execution time large enough. A
critical design choice, that makes CP non-trivial to use in practice, is the
branching decision, directing how the search space is explored. In this work,
we propose a general and hybrid approach, based on DRL and CP, for solving
combinatorial optimization problems. The core of our approach is based on a
dynamic programming formulation, that acts as a bridge between both techniques.
We experimentally show that our solver is efficient to solve two challenging
problems: the traveling salesman problem with time windows, and the 4-moments
portfolio optimization problem. Results obtained show that the framework
introduced outperforms the stand-alone RL and CP solutions, while being
competitive with industrial solvers
The one container drayage problem with soft time windows
Intermodal freight transport consists of using different modes of transport without changing the load unit. This results in a significant reduction in the time that goods spend at intermodal terminals, where transshipment takes place. Drayage refers to the transport of freight on trucks among intermodal terminals, depots, customers and suppliers. In spite of the fact that drayage only represents between 5 and 10 percent of total distance, it may amount up to more than 30 percent of the total costs. The aim of this work is to study drayage operations. First, an extensive literature review is undertaken. Since the intermodal transport chain can become more efficient by means of a proper organisation of the drayage movements, the optimization of the daily drayage problem has been identified as one of the main ways of reducing the drayage cost and improving intermodal operations. On this problem, the lack of a common benchmark has hindered reaching further conclusions from all the research carried out. Therefore, this paper proposes a common framework and presents a generalized formulation of the problem, which allows modeling most drayage policies, with the limitation of only considering one-container problems. Results show that flexible tasks in the repositioning of empty containers as well as soft time windows can reduce the operating costs and facilitate the management of drayage companies. This work may help consider adequate policies regarding drayage operations in intermodal terminals
Improving the Asymmetric TSP by Considering Graph Structure
Recent works on cost based relaxations have improved Constraint Programming
(CP) models for the Traveling Salesman Problem (TSP). We provide a short survey
over solving asymmetric TSP with CP. Then, we suggest new implied propagators
based on general graph properties. We experimentally show that such implied
propagators bring robustness to pathological instances and highlight the fact
that graph structure can significantly improve search heuristics behavior.
Finally, we show that our approach outperforms current state of the art
results.Comment: Technical repor
- …