Due to varying user demands in bicycle sharing systems, operators need to actively shift bikes between stations by a fleet of vehicles. We address the problem of finding efficient vehicle tours by an extended version of an iterated greedy construction heuristic following the concept of the PILOT method and GRASP and applying a variable neighborhood descend (VND) as local improvement. Computatio...

Using a heuristic optimization module based upon Variable Neighborhood Search (VNS), the system AutoGraphiX’s main feature is to find extremal or near extremal graphs, i.e., graphs that minimize or maximize an invariant. From the so obtained graphs, conjectures are found either automatically or interactively. Most of the features of the system relies on the optimization that must be efficient b...

In this work we extend a VNS for the periodic vehicle routing problem with time windows (PVRPTW) to a multiple VNS (mVNS) where several VNS instances are applied cooperatively in an intertwined way. The mVNS adaptively allocates VNS instances to promising areas of the search space. Further, an intertwined collaborative cooperation with a generic ILP solver applied on a suitable set covering ILP...

In this paper we study a complex real world workforce scheduling problem. We apply constructive search and variable neighbourhood search (VNS) metaheuristics and enhance these methods by using a variable fitness function. The variable fitness function (VFF) uses an evolutionary approach to evolve weights for each of the (multiple) objectives. The variable fitness function can potentially enhanc...

We report on the theory and implementation of a global optimization solver for general constrained nonlinear programming problems based on Variable Neighbourhood Search, and we give comparative computational results on several instances of continuous nonconvex problems. Compared to an efficient multi-start global optimization solver, the VNS solver proposed appears to be significantly faster.

In this work we present the extension of a variable neighborhood search (VNS) with the multilevel refinement strategy for periodic routing problems. The underlying VNS was recently proposed and performs already well on these problems. We apply a path based coarsening scheme by building fixed (route) segments of customers accounting for the periodicity. Starting at the coarsest level the problem...

We introduce the Three-Layer Hierarchical Ring Network Design Problem, which arises especially in the design of large telecommunication networks. The aim is to connect nodes that are assigned to three different layers using rings of bounded length. We present tailored Variable Neighborhood Search (VNS) and GRASP approaches to solve large instances of this problem heuristically, and discuss comp...

The aim of this paper is to propose a new heuristic for the Periodic Vehicle Routing Problem (PVRP) without time windows. The PVRP extends the classical Vehicle Routing Problem to a planning horizon of several days. Each customer requires a certain number of visits within this time horizon while there is some flexibility on the exact days of the visits. Hence, one has to choose the visit days f...

All commercial packages for vehicle routing that the authors are aware of use some form of variable neighbourhood search. This paper attempts to answer the question why this is the case. As we will show, variable neighbourhood search can be considered to be a very adaptable metaheuristic, which makes it especially suitable for the practical problems encountered in real life. We also point out t...

In this paper we present two major approaches to solve the car sequencing problem, in which the goal is to find an optimal arrangement of commissioned vehicles along a production line with respect to constraints of the form “no more than lc cars are allowed to require a component c in any subsequence of mc consecutive cars”. The first method is an exact one based on integer linear programming (...