Fabrizio Rossi

University of L'Aquila | Università dell'Aquila · Department of Information Engineering, Computer Science and Mathematics

The Lov\'asz theta function $\theta(G)$ provides a very good upper bound on the stability number of a graph $G$. It can be computed in polynomial time by solving a semidefinite program (SDP), which also turns out to be fairly tractable in practice. Consequently, $\theta(G)$ achieves a hard-to-beat trade-off between computational effort and strength...

A Coding DNA Sequence (CDS) is a fraction of DNA whose nucleotides are grouped into consecutive triplets called codons, each one encoding an amino acid. Because most amino acids can be encoded by more than one codon, the same amino acid chain can be obtained by a very large number of different CDSs. These synonymous CDSs show different features tha...

Background Machine learning (ML) represents a powerful tool to capture relationships between molecular alterations and cancer types and to extract biological information. Here, we developed a plain ML model aimed at distinguishing cancer types based on genetic lesions, providing an additional tool to improve cancer diagnosis, particularly for tumor...

Due to the increasing growth of the discipline Data Science, a partition into subdisciplines seems appropriate. Therefore, we propose the division of Data Science in Pure Data Science, in which methods and tools are developed, and Applied Data Science, in which these methods and tools are adapted and applied to practical problems of a specific doma...

We present a data-driven solution to manage visitors’ access at the Uffizi Gallery in Florence, Italy. The goal is to avoid the long lines outside the Museum, improving not only visitors’ experience, but also decency and security in the urban area. The solution implements a queue management system based on two data analytics models, one predictive...

Forecasting volumes of incoming calls is the first step of the workforce planning process in call centers and represents a prominent issue from both research and industry perspectives. We investigate the application of Neural Networks to predict incoming calls 24 hours ahead. In particular, a Machine Learning deep architecture known as Echo State N...

This paper highlights humans' social and mobility behaviors' role in the continuous engineering of sustainable socio-technical systems. Our approach relates the humans' characteristics and intentions with the system's goals, and models such interaction. Such a modeling approach aligns the architectural design and associated quality of service (QoS)...

Forecasting volumes of incoming calls is the first step of the workforce planning process in call centers and represents a prominent issue from both research and industry perspectives. We investigate the application of Neural Networks to predict incoming calls 24 hours ahead. In particular, a Deep Learning method known as Echo State Networks, is co...

Cutting planes have been an important factor in the impressive progress made by integer programming (IP) solvers in the past two decades. However, cutting planes have had little impact on improving performance for symmetric IPs. Rather, the main breakthroughs for solving symmetric IPs have been achieved by cleverly exploiting symmetry in the enumer...

The stable set problem is a fundamental combinatorial optimisation problem, that is known to be very difficult in both theory and practice. Some of the solution algorithms in the literature are based on 0-1 linear programming formulations. We examine an entire family of such formulations, based on so-called clique and nodal inequalities. As well as...

The Capacitated Facility Location Problem calls for opening a set of facilities with capacity constraints, with the aim of satisfying at the minimum cost the demands of a set of customers. We present a new class of valid inequalities, the Weak Flow Cover inequalities. We show that Weak Flow Cover inequalities can be separated in polynomial time and...

A γ-quasi-clique is a simple and undirected graph with edge density of at least γ. Given a graph G, the maximum γ-quasi-clique problem (γ-QCP) consists of finding an induced γ-quasi-clique with the maximum number of vertices. γ-QCP generalizes the well-known maximum clique problem and its solution is useful for detecting dense subgraphs. After revi...

The problem of choosing an optimal codon sequence arises when synthetic protein-coding genes are added to cloning vectors for expression within a non-native host organism: to maximize yield, the chosen codons should have a high frequency in the host genome, but particular nucleotide bases sequences (called “motifs”) should be avoided or, instead, i...

We address some special cases of job shop and flow shop scheduling problems with s-precedence constraints. Unlike the classical setting, in which precedence constraints among the tasks of a job are finish–start, here the task of a job cannot start before the task preceding it has started. We give polynomial exact algorithms for the following proble...

Clique inequalities appear in linear descriptions of many combinatorial optimisation problems. In general, they form an exponential family and, in addition, the associated separation problem is strongly NP-hard, being equivalent to a maximum weight clique problem. Therefore, most of the known (both exact and heuristic) separation procedures follow...

The goal of radiotherapy is to cover a target area with a desired radiation dose while keeping the exposition of non-target areas as low as possible in order to reduce radiation side effects. In the case of Intensity Modulated Proton Therapy (IMPT), the dose distribution is typically designed via a treatment planning optimisation process based on c...

We study the shift scheduling problem in a multi-shift, flexible call center. Differently from previous approaches, the staffing levels ensuring the desired quality of service are considered uncertain, leading to a two-stage robust integer program with right-hand-side uncertainty. We show that, in our setting, modeling the correlation of the demand...

The stable set problem is a well-known NP-hard combinatorial optimization problem. As well as being hard to solve (or even approximate) in theory, it is often hard to solve in practice. The main difficulty is that upper bounds based on linear programming (LP) tend to be weak, whereas upper bounds based on semidefinite programming (SDP) take a long...

A new exact approach to the stable set problem is presented, which attempts to avoid the pitfalls of existing approaches based on linear and semidefinite programming. The method begins by constructing an ellipsoid that contains the stable set polytope and has the property that the upper bound obtained by optimising over it is equal to the Lov�asz t...

We propose a robust optimization model for shift scheduling in call centers. The model is designed to react to the deviations that often occur between the planned staffing levels and the actual number of employees that would be necessary to guarantee the desired level of service. Different perturbation patterns are considered giving rise to differe...

The problem of finding the shortest path between two points underlies the concept of distance. In the common understanding, the physical distance between two points is always regarded as a non-negative quantity. However, from a mathematical point of view, the shortest-path problem can be defined and solved even when distances between points are neg...

The famous Lovász theta number θ(G)θ(G) is expressed as the optimal solution of a semidefinite program. As such, it can be computed in polynomial time to an arbitrary precision. Nevertheless, computing it in practice yields some difficulties as the size of the graph gets larger and larger, despite recent significant advances of semidefinite program...

A great deal of research has been focusing, since the early seventies, on finding strong relaxations for the stable set problem. Polyhedral combinatorics techniques have been at first developed to strengthen the natural linear formulation. Afterward, strong semidefinite programming relaxations have been deeply investigated. Nevertheless, the result...

In this note, we use a reduction by Cornaz and Jost from the graph (max-)coloring problem to the maximum (weighted) stable set problem in order to characterize new graph classes where the graph coloring problem and the more general max-coloring problem can be solved in polynomial time.

The data exchange between ground stations and satellite constellations is becoming a challenging task, as more and more communication requests must be daily scheduled on a few, expensive stations located all around the Earth. Most of the scheduling procedures adopted in practice cannot cope with such complexity, and the development of optimization-...

A new exact approach to the stable set problem is presented, which attempts to avoids the pitfalls of existing approaches based on linear and semidefinite programming. The method begins by constructing an ellipsoid that contains the stable set polytope and has the property that the upper bound obtained by optimising over it is equal to the Lovász t...

Computing the 1-width of the incidence matrix of a Steiner Triple System gives rise to highly symmetric and computationally challenging set covering problems. The largest instance solved so far corresponds to a Steiner Tripe System of order 81. We present optimal solutions for systems of orders 135 and 243. These are computed by a tailored implemen...

We introduce orbital branching, an effective branching method for integer programs containing a great deal of symmetry. The method is based on computing groups of variables that are equivalent with respect to the symmetry remaining in the problem after branching, including symmetry which is not present at the root node. These groups of equivalent v...

Synchronous Digital Hierarchy (SDH) is a standard for data transmission over telecommunication networks which is often used for framing and synchronization at the physical layer. SDH networks can carry large payloads, but, at the same time, accommodate lower speed signals packed into elementary transport units. The price of this flexibility consist...

Although the lift-and-project operators of Lovász and Schrijver have been the subject of intense study, their M(K, K) operator has received little attention. We consider an application of this operator to the stable set problem. We begin with an initial linear programming (LP) relaxation consisting of clique and non-negativity inequalities, and the...

We investigate a planning problem arising in the forthcoming digital video broadcasting (DVB-T) system. Unlike current analog systems, the DVB-T standard allows a mitigation of the interference by means of a suitable synchronization of the received signals. The problem we describe in this paper is that of finding a time offset to impose to the sign...

Orbital branching is a method for branching on variables in integer programming that reduces the likelihood of evaluating redundant, isomorphic nodes in the branch-and-bound procedure. In this work, the orbital branching methodology is extended so that the branching disjunction can be based on an arbitrary constraint. Many important families of int...

We introduce orbital branching, an effective branching method for integer programs containing a great deal of symmetry. The method is based on computing groups of variables that are equivalent with respect to the symmetry remaining in the problem after branching, including symmetry that is not present at the root node. These groups of equivalent va...

Without Abstract

The introduction of digital terrestrial broadcasting all over Europe requires a com-plete and challenging re-planning of in-place analog systems. But an abrupt mi-gration of resources (transmitters and frequencies) from analog to digital networks cannot be accomplished, since the analog services must be preserved temporar-ily. Hence, a multi-networ...

An important problem arising in the management of logistic networks is the following: given a set of activities to be performed, each requiring a set of resources, select the optimal set of resources compatible with the system capacity constraints. This problem is called Batch Selection Problem (BSP) from traditional applications to flexible manufa...

This paper presents a decision support tool for solving a cutting and reuse problem arising in a European plant devoted to the production of gear belts. In this production, rectangular pieces of rubberised nylon are cut using machines employing parallel blades, so as to obtain rectangular components of identical height and (possibly) different widt...

We propose a branch-and-cut algorithm for the Maximum Cardinality Stable Set problem. Rank constraints of general structure are generated by executing clique separation algorithms on a modified graph obtained with edge projections. A branching scheme exploiting the available inequalities is also introduced. A computational experience on the DIMACS...

Air traffic flow management (ATFM) consists of several activities performed by control authorities in order to reduce delays due to traffic congestion. Ground holding decisions restrict certain flights from tacking off at the scheduled departure time if congestion is expected at the destination airport. They are motivated by the fact that it is saf...

The service provided by a Digital Video Broadcasting (DVB) system in terms of coverage of territory and population is greatly affected by transmitters emission power and temporal offset. We show that the problem of computing the emission powers so as to guarantee the required signal to interference ratio can be formulated as a mixed integer linear...

Research studies on multi-agent systems have been recently boosted by manufacturing and logistics with deep motivations like the presence of independent human deciders with individual goals, the aspiration to dominate the complexity of decision-making in large organizations, the simplicity and robustness of self-reacting distributed systems. After...

Research studies on multi-agent systems have been recently boosted by manufacturing and logistics with deep motivations like the presence of independent human deciders with individual goals, the aspiration to dominate the complexity of decision-making in large organizations, the simplicity and robustness of self-reacting distributed systems. After...

We address a design problem that arises when a circular architecture is adopted to move resources in a system. In many of such architectures the demand directed from one node to another affects all the intermediate nodes, involving costs which increase both with the number of nodes and with the demand volume. We consider an application to network d...

Distributing material flows among the workstations of a plant is a crucial problem in order to reduce both production and logistics costs, especially when product mix and volume production are very large. Optimal solutions should meet due dates requirements while assigning operations in accordance to the production capacity available at the moment....

This paper deals with the problem of makespan minimization in a flow shop with two machines when the input buffer of the second machine can only host a limited number of parts. Here we analyze the problem in the context of batch processing, i.e., when identical parts must be processed consecutively. We propose an exact branch-and-bound algorithm, i...

This paper deals with a sequencing problem arising in the management of paced-flowlines, that is production lines where jobs are released at constant time intervals. The problem is to sequence jobs to minimize total tardiness. The problem can be formulated as an assignment problem with a number of knapsack constraints. We prove the strong NP-hardne...

This paper deals with the material flow management in a large-scale manufacturing process, namely the assembly of automobiles in a highly automated plant in Italy. After a detailed description of the plant from the viewpoint of material flow issues, the modeling process and the methodologies employed to address the problems are illustrated. The dec...

This paper deals with the problem of makespan minimization in a flow shop with two machines when the input buffer of the second machine can only host a limited number c of parts. This problem has been shown to be NP-hard for any c > 0 and c < n-1, where n is the number of jobs, by Papadimitriou and Kanellakis (1980). Here we analyze the problem in...

This paper deals with the problem of part input sequencing in an automated flow shop system. The system consists of one input/output station, two machines and one AGV, which is used for all part transfer operations throughout the cell. The objective is the minimization of the makespan. This cell architecture has recently received considerable atten...

In this paper we examine the issue of tool management in a flexible manufacturing cell. The type of system considered here is typical of mechanical manufacturing, in which large metallic parts are loaded on the machines and are not moved until processing completion. The architecture of the cell is characterized by the absence of on-board tool magaz...

In a plant for automobile assembly, sub-assemblies are produced in shops consistingof sequential groups of parallel workstations. The problem of optimally sequencing n jobs in such an environmentis a generalization of the flow shop problem. In this paper a new dispatching rule is proposed that also considersjobs that have not yet completed the prev...

We report on the application of Integer Programming to support the frequency coordination among France and Italy in December 2007. The problem is derived from the standard network planning problem by adding two families of complicating constraints. This results in difficult Mixed Integer Linear Programs. We tackle such problems by a tailored MIP he...