1,721,132 research outputs found
The Multi-Vehicle Traveling Purchaser Problem with Pairwise Incompatibility Constraints and Unitary Demands: A Branch-and-Price Approach
No full textIn this work we study a suppliers selection and routing problem where a fleet of
homogeneous vehicles with a predefined capacity is available for procuring different products from
different suppliers with the aim to minimize both the traveling and the purchasing costs. Decisions are
further complicated by the presence of pairwise incompatibility constraints among products, implying
the impossibility of loading two incompatible products on the same vehicle. The problemis known as
the Multi-Vehicle Traveling Purchaser Problem with Pairwise Incompatibility Constraints.We study a
variant in which products demand is unitary and propose a column generation approach based on a
Dantzig-Wolfe reformulation of the problem, where each column represents a feasible vehicle route
associated with a compatible purchasing plan.Two different procedures are introduced to solve the
pricing problem, namely a labeling algorithm solving a Resource-Constrained Elementary Shortest
Path Problem on an expanded graph, and a tailored branch-and-cut algorithm. Due to the integrality
request on variables, we embed the column generation in a branch-and-bound framework and propose
different branching rules, thus obtaining a branch-and-price procedure. Extensive tests, carried out on
a large set of instances, show that our branch-and-price method performs well, improving on average,
both in quality and in computational time, solutions obtained by a branch-and-cut approach existing in
the literature that relies on a three-index connectivity constraints based formulation
The Multi-Vehicle Traveling Purchaser Problem with Pairwise Incompatibility Constraints and Unitary Demands: A Branch-and-Price Approach
No full textIn this work we study a suppliers selection and routing problem where a fleet of
homogeneous vehicles with a predefined capacity is available for procuring different products from
different suppliers with the aim to minimize both the traveling and the purchasing costs. Decisions are
further complicated by the presence of pairwise incompatibility constraints among products, implying
the impossibility of loading two incompatible products on the same vehicle. The problemis known as
the Multi-Vehicle Traveling Purchaser Problem with Pairwise Incompatibility Constraints.We study a
variant in which products demand is unitary and propose a column generation approach based on a
Dantzig-Wolfe reformulation of the problem, where each column represents a feasible vehicle route
associated with a compatible purchasing plan.Two different procedures are introduced to solve the
pricing problem, namely a labeling algorithm solving a Resource-Constrained Elementary Shortest
Path Problem on an expanded graph, and a tailored branch-and-cut algorithm. Due to the integrality
request on variables, we embed the column generation in a branch-and-bound framework and propose
different branching rules, thus obtaining a branch-and-price procedure. Extensive tests, carried out on
a large set of instances, show that our branch-and-price method performs well, improving on average,
both in quality and in computational time, solutions obtained by a branch-and-cut approach existing in
the literature that relies on a three-index connectivity constraints based formulation
Heuristics for the traveling salesman problem with pickup and delivery
No full textWe consider the Traveling Salesman Problem with Pickup and Delivery (TSPPD), an extension of the well-known Traveling Salesman Problem where each customer to be served is associated with two quantities of goods to be collected and delivered, respectively. A vehicle with given capacity starts at a depot and must visit each customer exactly once. The vehicle capacity must not be exceeded and the total length of the tour must be minimized. We describe new heuristics for TSPPD, the first based on the exact solution of a special case and the second based on tabu search, and we analyze their average performance through extensive computational experiments
A column generation approach for the Multi-Vehicle Travelling Purchaser Problem with Pairwise Incompatibility Constraints
No full textIntroducing incompatibility restrictions among products in a multi-vehicle procurement and routing context
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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