The synchronized multi-commodity multi-service Transshipment-Hub Location Problem with cyclic schedules

The synchronized multi-commodity multi-service Transshipment-Hub Location Problem is a hub location problem variant faced by a logistics service provider operating in the context of synchromodal logistics. The provider must decide where and when to locate transshipment facilities in order to manage many customers’ origin–destination shipments with release and due dates while minimizing a total cost given by location costs, transportation costs, and penalties related to unmet time constraints. The considered synchromodal network involves different transportation modes (e.g., truck, rail, river and sea navigation) to perform long-haul shipments and the freight synchronization at facilities for transshipment operations. To the best of our knowledge, this variant has never been studied before. Considering a time horizon in which both transportation services and demand follow a cyclic pattern, we propose a time–space network representation of the problem and an ad-hoc embedding of the time-dependent parameters into the network topology and the arcs’ weight. This allows to model the flow synchronization required by the problem through a Mixed-Integer Linear Programming formulation with a simplified structure, similar to well-known hub location problems and avoiding complicating constraints for managing the time dimension. Through an extensive experimental campaign conducted over a large set of realistic instances, we present a computational and an economic analysis. In particular, we want to assess the potential benefits of implementing synchromodal logistics operations into long-haul supply-chains managed by large service providers. Since flexibility is one of the main features of synchromodality, we evaluate the impact on decisions and costs of different levels of flexibility regarding terminals’ operations and customers’ requirements

Heuristics for the two-echelon vehicle routing problem: A multi-start approach

Tech. Rep. CIRRELT-2011-16, CIRRELT, Montreal, Canad

A greedy adaptive search procedure for multi-dimensional multi-container packing problems

Tech. Rep. CIRRELT-2012-10, CIRRELT, Montrea

The symplectic Deligne-Mumford stack associated to a stacky polytope

We discuss a symplectic counterpart of the theory of stacky fans. First, we define a stacky polytope and construct the symplectic Deligne-Mumford stack associated to the stacky polytope. Then we establish a relation between stacky polytopes and stacky fans: the stack associated to a stacky polytope is equivalent to the stack associated to a stacky fan if the stacky fan corresponds to the stacky polytope.Comment: 20 pages; v2: To appear in Results in Mathematic

GRASP with path relinking for the two-echelon vehicle routing problem

Tech. Rep. CIRRELT-2012-45, CIRRELT, Montrea

Humans versus robots: Converting golf putter trajectories for robotic guidance

Robotic devices are used to provide physical guidance when teaching different movements. To advance our knowledge of robotic guidance in training complex movements, this investigation tested different kinematic data filtering methods of individual’s golf putts to convert them into trajectories to be employed by a robot arm. The purpose of the current study was to identify a simple filtering method to aptly replicate participants’ individual golf putter trajectories which could be used by the robot to execute them with greater consistency and accuracy than their human counterpart. Participants putted towards 3 targets where three-dimensional data of the putter’s head was filtered and then fitted by using one- or two-dimensions of the participant’s putter head trajectories. As expected, both filtering methods employed with the robot outperformed the human participants in ball endpoint accuracy and consistency. Further, after comparing the filtered to the human participants trajectories, the two-dimensional method best replicated the kinematic features of human participants natural putter trajectory, while the one-dimensional method failed to replicate participant’s backstroke position. This investigation indicates that a two-dimensional filtering method, using Y-forward and Z-vertical position data, can be used to create accurate, consistent, and smooth trajectories delivered by a robot arm

Worst-case analysis for new online bin packing problems

We consider two new online bin packing problems, the online Variable Cost and Size Bin Packing Problem (o-VCSBPP) and the online Generalized Bin Packing Problem (o-GBPP). We take two well-known bin packing algorithms to address them, the First Fit (FF) and the Best Fit (BF). We show that both algorithms have an asymptotic worst-case ratio bound equal to 2 for the o-VCSBPP and this bound is tight. When there are enough bins of a particular type to load all items, FF and BF also have an absolute worst-case ratio bound equal to 2 for the o-VCSBPP, and this bound is also tight. In addition, we prove that no worst-case ratio bound of FF and BF can be computed for the o-GBPP. Therefore, we consider a natural evolution of these algorithms, the First Fit with Rejection and the Best Fit with Rejection, able to reject inconvenient bins at the end of the process. Similarly, we prove that no worst-case ratio of these algorithms can be computed for the o-GBPP. Finally, we give sucient conditions under which algorithms do not admit any performance ratio, and conclude that the worst-case results obtained for the o-VCSBPP and the o-GBPP also hold for the oine variant of these two problems

The generalized bin packing problem

Tech. Rep. CIRRELT 2011-39, CIRRELT, Montreal, Canad