178,391 research outputs found
Dynamic ng-path relaxation for the delivery man problem
No full textThe ng-path relaxation was introduced by Baldacci, Mingozzi, and Roberti [Baldacci R, Mingozzi A, Roberti R (2011) New route relaxation and pricing strategies for the vehicle routing problem. Oper. Res. 59(5):1269–1283] for computing tight lower bounds to vehicle routing problems by solving a relaxation of the set-partitioning formulation, where routes are not necessarily elementary and can contain predefined subtours. The strength of the achieved lower bounds depends on the subtours that routes can perform. In this paper, we introduce a new general bounding procedure called dynamic ng-path relaxation that enhances the one of Baldacci, Mingozzi, and Roberti (2011) by iteratively redefining the subtours that routes can perform. We apply the bounding procedure on the well-known delivery man problem, which is a generalization of the traveling salesman problem where costs for traversing arcs depend on their positions along the tour. The proposed bounding procedure is based on column generation and computes a sequence of nondecreasing lower bounds to the problem. The final lower bound is used to solve the problem to optimality with a simple dynamic programming recursion. An extensive computational analysis on benchmark instances from the TSPLIB shows that the new bounding procedure yields better lower bounds than those provided by the method of Baldacci, Mingozzi, and Roberti (2011). Furthermore, the proposed exact method outperforms other exact methods recently presented in the literature and is able to close five open instances with up to 150 vertices
Container Stowage Planning - k-shift instances - Roberti-Parenno
No full textThis dataset includes all the instances for the k-shift container stowage planning problem from the papers:
Parreño-Torres, C., Çalık, H., Alvarez-Valdes, R., & Ruiz, R. (2021). Solving the generalized multi-port container stowage planning problem by a matheuristic algorithm. Computers and Operations Research, 133, 105383. https://doi.org/10.1016/j.cor.2021.105383
Roberti, R., & Pacino, D. (2018). A decomposition method for finding optimal container stowage plans. Transportation Science, 52(6), 1444–1462. https://doi.org/10.1287/trsc.2017.0795
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Roberti (Giovanni). La Eloquenza Greca II.
No full textHarmand R. Roberti (Giovanni). La Eloquenza Greca II.. In: Revue des Études Grecques, tome 9, fascicule 34,1896. pp. 351-352
Valutazione della tenacità a frattura di un acciaio inossidabile bifasico austenitico-ferritico mediante l'integrale J
No full textUn modello fisico matematico dell'arrotondamento dell'apice della cricca: applicazione ad un acciaio strutturale al C-Mn
No full textOptimal Scheduling of Railway Track Possessions in Large-Scale Projects with Multiple Construction Works
No full textThis paper addresses the railway track possession scheduling problem (RTPSP), where a large-scale railway infrastructure project consisting of multiple construction works is to be planned. The RTPSP is to determine when to perform the construction works and in which track possessions while satisfying different operational constraints and minimizing the total construction cost. To find an optimal solution of the RTPSP, this paper proposes an approach that, first, transfers the nominal market prices into track-possession-based real prices, and then generates a schedule of the construction works by solving a mixed-integer linear-programming model for the given track blocking proposal. The proposed approach is tested on a real-life case study from the Danish railway infrastructure manager. The results show that, in 2 h of computing time, the approach is able to provide solutions that are within 0.37% of the optimal one for six different blocking proposals and two alternative construction providers, so it can be used as an effective support tool in the primary planning stage to suggest preferable track possessions within the existing railway services
New route relaxation and pricing strategies for the vehicle routing problem
No full textIn this paper, we describe an effective exact method for solving both the capacitated vehicle routing problem (cvrp) and
the vehicle routing problem with time windows (vrptw) that improves the method proposed by Baldacci et al. [Baldacci,
R., N. Christofides, A. Mingozzi. 2008. An exact algorithm for the vehicle routing problem based on the set partitioning
formulation with additional cuts. Math. Programming 115(2) 351–385] for the cvrp. The proposed algorithm is based
on the set partitioning (SP) formulation of the problem. We introduce a new route relaxation called ng-route, used by
different dual ascent heuristics to find near-optimal dual solutions of the LP-relaxation of the SP model. We describe a
column-and-cut generation algorithm strengthened by valid inequalities that uses a new strategy for solving the pricing
problem. The new ng-route relaxation and the different dual solutions achieved allow us to generate a reduced SP problem
containing all routes of any optimal solution that is finally solved by an integer programming solver. The proposed method
solves four of the five open Solomon’s vrptw instances and significantly improves the running times of state-of-the-art
algorithms for both vrptw and cvrp
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