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This paper addresses a variation of the traveling salesman problem with pickup and delivery in which loading and unloading operations have to be executed in a LIFO (Last-in-First-Out) order. We introduce three new local search operators for this problem which are then embedded within a variable neighborhood search heuristic. We evaluate the performance of… (More)

This paper studies the double traveling salesman problem with two stacks. A number of requests have to be served where each request consists in the pickup and delivery of an item. All the pickup operations have to be performed before any delivery can take place. A single vehicle is available that starts from a depot, performs all the pickup operations and… (More)

We study a variant of the spanning tree problem where we require that, for a given connected graph, the spanning tree to be found has the minimum number of branch vertices (that is vertices of the tree whose degree is greater than two). We provide four different formulations of the problem and compare different relaxations of them, namely lagrangian… (More)

This paper introduces an additive branch-and-bound algorithm for two variants of the pickup and delivery traveling salesman problem in which loading and unloading operations have to be performed either in a Last-In-First-Out (LIFO) or in a First-In-First-Out (FIFO) order. Two relaxations are used within the additive approach: the assignment problem and the… (More)

Given a graph G where a label is associated with each edge, we address the problem of looking for a maximum matching of G using the minimum number of different labels, namely the Labeled Maximum Matching Problem. It is a relatively new problem whose application is related to the timetabling problem [15]. We prove it is NP-complete and present four different… (More)

Given an undirected and vertex weighted graph G, the Weighted Feedback Vertex Problem (WFVP) consists in finding a subset F ⊆ V of vertices of minimum weight such that each cycle in G contains at least one vertex in F. The WFVP on general graphs is known to be NP-hard. In this paper we introduce a new class of graphs, namely the diamond graphs, and give a… (More)

Given an undirected and vertex weighted graph G = (V, E, w), the Weighted Feedback Vertex Problem (WFVP) consists of finding a subset F ⊆ V of vertices of minimum weight such that each cycle in G contains at least one vertex in F. The WFVP on general graphs is known to be NP-hard and to be polynomially solvable on some special classes of graphs (e.g.,… (More)

Given a vertex weighted graph G, a minimum Weighted Feedback Vertex Set (MWFVS) is a subset F ⊆ V of vertices of minimum weight such that each cycle in G contains at least one vertex in F. The MWFVS on general graph is known to be NP-hard. In this paper we introduce a new class of graphs, namely the diamond graphs, and give a linear time algorithm to solve… (More)

Given an undirected and vertex weighted graph G = (V, E, w), the Weighted Feedback Vertex Set Problem consists of finding the subset F ⊆ V of vertices, with minimum weight, whose removal results in an acyclic graph. Finding the minimum feedback vertex set in a graph is an important combinato-rial problem that has a variety of real applications. In this… (More)

Wireless sensor networks are generally composed of a large number of hardware devices of the same type, deployed over a region of interest in order to perform a monitoring activity on a set of target points. Nowadays, several different types of sensor devices exist, which are able to monitor different aspects of the region of interest (including sound,… (More)