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ALBERTO LOCATELLI

Ricercatore t.d. art. 24 c. 3 lett. A
Dipartimento di Scienze e Metodi dell'Ingegneria

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Pubblicazioni

2023 - A GRASP for a real-world scheduling problem with unrelated parallel print machines and sequence-dependent setup times [Articolo su rivista]
Iori, M.; Locatelli, A.; Locatelli, M.
abstract

We consider a real-world scheduling problem arising in the colour printing industry. The problem consists in assigning print jobs to a heterogeneous set of flexographic printer machines and finding a processing sequence for the jobs assigned to each machine. The machines are characterised by a limited sequence of colour groups and can equip additional components (e.g. embossing rollers and perforating rolls) to process jobs that require specific treatments. The process to equip a machine with an additional component or to clean a colour group takes a long time, with the effect of significantly raising the setup times. The aim is to minimise a weighted sum of total weighted tardiness and total setup time. The problem derives from the activities of an Italian food packaging company. To solve it, we developed a greedy randomised adaptive search procedure equipped with several local search procedures. The excellent performance of the algorithm is proved by extensive computational experiments on real-world instances, for which it produced good-quality solutions within a limited computing time. The algorithm is currently in use at the company to support their weekly scheduling decisions.

2022 - Knapsack problems — An overview of recent advances. Part I: Single knapsack problems [Articolo su rivista]
Cacchiani, V.; Iori, M.; Locatelli, A.; Martello, S.
abstract

After the seminal books by Martello and Toth (1990) and Kellerer, Pferschy, and Pisinger (2004), knapsack problems became a classical and rich research area in combinatorial optimization. The purpose of this survey, which is structured in two parts, is to cover the developments that appeared in this field after the publication of the latter volume. Part I is devoted to problems whose goal is to optimally assign items to a single knapsack. Besides the classical knapsack problems (binary, subset sum, bounded, unbounded, change-making), we review problems with special constraints (setups, multiple-choice, conflicts, precedences, sharing, compartments) as well as relatively recent fields of investigation, like robust and bilevel problems. The subsequent Part II covers multiple, multidimensional, and quadratic knapsack problems, and includes a succinct treatment of online and multiobjective knapsack problems.

2022 - Knapsack problems — An overview of recent advances. Part II: Multiple, multidimensional, and quadratic knapsack problems [Articolo su rivista]
Cacchiani, V.; Iori, M.; Locatelli, A.; Martello, S.
abstract

After the seminal books by Martello and Toth (1990) and Kellerer, Pferschy, and Pisinger (2004), knapsack problems became a classical and rich research area in combinatorial optimization. The purpose of this survey, structured in two parts, is to cover the developments appeared in this field after the publication of the latter volume. Part I treats the classical single knapsack problems and their variants. The present Part II covers multiple, multidimensional, and quadratic knapsack problems, as well as other relevant variants, such as, e.g., multiobjective and online versions.

2022 - Tool Switching Problems in the Context of Overlay Printing with Multiple Colours [Relazione in Atti di Convegno]
Iori, M.; Locatelli, A.; Locatelli, M.; Salazar-Gonzalez, J. -J.
abstract

This paper addresses problems arising in the context of overlay printing with multiple colours, where a finite set of jobs must be sequentially performed by a printing machine which can simultaneously accommodate a limited number of colours. Each job is associated with a subset of colours that the machine must have stored in its magazine before starting the execution. Thus, some colour switches may be required between the execution of two consecutive jobs. Since colour switches imply a reduction of productivity, minimizing them is desirable. In this regard, we address three distinct problems of increasing difficulty. All these problems can be seen as variants of the Tool Switching Problem, where each colour is treated as a tool. For each problem we discuss its complexity and propose a mathematical programming model. We evaluate the effectiveness of the models on several instances that have been generated with the aim of covering different scenarios of interest.

2021 - Scheduling of Parallel Print Machines with Sequence-Dependent Setup Costs: A Real-World Case Study [Relazione in Atti di Convegno]
Iori, M.; Locatelli, A.; Locatelli, M.
abstract

In the present work, we consider a real-world scheduling problem arising in the color printing industry. The problem consists in assigning print jobs to a heterogeneous set of flexographic printer machines, as well as in finding a processing sequence for the sets of jobs assigned to each printer. The aim is to minimize a weighted sum of total weighted tardiness and total setup times. The machines are characterized by a limited sequence of color groups and can equip additional components (e.g., embossing rollers and perforating rolls) to process jobs that require specific treatments. The process to equip a machine with an additional component or to clean a color group takes a long time, with the effect of significantly raising the setup costs. Furthermore, the time required to clean a color group between two different jobs depends directly on the involved colors. To tackle the problem, we propose a constructive heuristic followed by some local search procedures that are used one after the other in an iterative way. Extensive tests on real-world instances prove that the proposed algorithm can obtain very good-quality solutions within a limited computing time.