M. Grazia Speranza | University of Brescia (original) (raw)
Papers by M. Grazia Speranza
RePEc: Research Papers in Economics, 2017
Multi-compartment vehicle routing problems arise in a variety of problem settings in which differ... more Multi-compartment vehicle routing problems arise in a variety of problem settings in which different product types have to be transported separated from each other. In this paper, a problem variant which occurs in the context of glass waste recycling is considered. In this problem, a set of locations exists, each of which offering a number of containers for the collection of different types of glass waste (e.g. colorless, green, brown glass). In order to pick up the contents from the containers, a fleet of homogeneous disposal vehicles is available. Individually for each disposal vehicle, the capacity can be discretely separated into a limited number of compartments to which different glass waste types are assigned. The objective of the problem is to minimize the total distance to be travelled by the disposal vehicles. For solving this problem to optimality, a branch-and-cut algorithm has been developed and implemented. Extensive numerical experiments have been conducted in order to evaluate the algorithm and to gain insights into the problem structure. The corresponding results show that the algorithm is able to solve instances with up to 50 locations to optimality and that it reduces the computing time by 87% compared to instances from the literature. Additional experiments give managerial insights into the use of different variants of compartments with flexible sizes.
Transportation Research Part C: Emerging Technologies
A massive use of electric vehicles is nowadays considered to be a key element of a sustainable tr... more A massive use of electric vehicles is nowadays considered to be a key element of a sustainable transportation policy and the availability of charging stations is a crucial issue for their extensive use. Charging stations in an urban area have to be deployed in such a way that they can satisfy a demand that may dramatically vary in space and time. In this paper we present an optimization model for the location of charging stations that takes into account the main specific features of the problem, in particular the different charging technologies, and their associated service time, and the fact that the demand depends on space and time. To measure the importance of incorporating the time dependence in an optimization model, we also present a simpler model that extends a classical location model and does not include the temporal dimension. A worst-case analysis and extensive computational experiments show that ignoring the temporal dimension of the problem may lead to a substantial amount of unsatisfied demand.
4OR, 2020
In Vehicle Routing Problems (VRPs) the decisions to be taken concern the assignment of customers ... more In Vehicle Routing Problems (VRPs) the decisions to be taken concern the assignment of customers to vehicles and the sequencing of the customers assigned to each vehicle. Additional decisions may need to be jointly taken, depending on the specific problem setting. In this paper, after discussing the different kinds of decisions taken in different classes of VRPs, the class where the decision about when the routes start from the depot has to be taken is considered and the related literature is reviewed. This class of problems, that we call VRPs over time, includes the periodic routing problems, the inventory routing problems, the vehicle routing problems with release dates, and the multi-trip vehicle routing problems.
Transportation Research Procedia, 2022
The class of inventory routing problems (IRP) includes a variety of different optimization prob-l... more The class of inventory routing problems (IRP) includes a variety of different optimization prob-lems that, though often very different from each other, all consider a routing and an inventory component of an optimization problem. Time may be discrete or continuous, demand may be deterministic or stochastic, inventory holding costs may be accounted for in the objective
EURO Journal on Decision Processes, 2019
In this paper, we analyze and discuss the optimization challenges and opportunities raised by the... more In this paper, we analyze and discuss the optimization challenges and opportunities raised by the decision of building an automated clinical laboratory in a hospital unit. We first describe the general decision setting from a strategic, tactical and operational perspective. We then focus on the analysis of a practical case, i.e., the Central Laboratory of a large urban academic teaching hospital in the North of Italy, the 'Spedali Civili' in Brescia. We will describe the present situation and the research opportunities related to the study of possible improvements of the management of the laboratory.
European Journal of Operational Research, 2018
Computers & Operations Research
Lecture Notes in Economics and Mathematical Systems, 2009
imply, even in the absence of a specific statement, that such names are exempt from the relevant ... more imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
European Journal of Operational Research, 1987
This paper proposes a discrete-time heterogeneous model to represent the interaction between the ... more This paper proposes a discrete-time heterogeneous model to represent the interaction between the dynamic arrival process of multiple TCP sources and a bottleneck queue. It utilises a novel time-variant calculation approach for transient queueing models, which modifies the conventional steady-state method by no longer requiring the equilibrium assumption. The main contributions are: (1) The limitation of the conventional queueing method is analysed and the benefits of the proposed modification is demonstrated; (2) The proposed dynamic arrival process of multiple sources is illustrated, which interacts with the queueing process and statistically responds to the positive and negative congestion feedback; (3) The fidelity of the proposed model is extensively validated by the closely matched results from MATLAB numerical solutions and NS-2 discrete-event simulation experiments.
Many cities and towns offer nowadays to citizens a bike sharing system (BSS). When a company star... more Many cities and towns offer nowadays to citizens a bike sharing system (BSS). When a company starts the service, several decisions have to be taken on the location and size of the rental stations, and the number of vehicles to use to re-balance the bikes in the stations, in addition to the cost and policies for the payment of the service. Also, when the service is in place, it is often necessary to modify it, in many cases to expand it. In this paper, starting from the experience gained in a real-case application, we present a simulation framework to support the tactical decisions in the design or revision of a BSS. We will also present the application of the framework to the case of Bicimia in Brescia, Italy.
European Journal of Operational Research, 2016
We consider a setting in which a company not only has a fleet of capacitated vehicles and drivers... more We consider a setting in which a company not only has a fleet of capacitated vehicles and drivers available to make deliveries, but may also use the services of occasional drivers who are willing to make a single delivery using their own vehicle in return for a small compensation if the delivery location is not too far from their own destination. The company seeks to make all the deliveries at minimum total cost, i.e., the cost associated with its own vehicles and drivers plus the compensation paid to the occasional drivers. The option to use occasional drivers to make deliveries gives rise to a new and interesting variant of the classical capacitated vehicle routing problem. We design and implement a multi-start heuristic which produces solutions with small errors when compared with optimal solutions obtained by solving an integer programming formulation with a commercial solver. A comprehensive computational study provides valuable insight into the potential of using occasional drivers to reduce delivery costs, focusing primarily on the number and flexibility of occasional drivers and the compensation scheme employed.
EURO Advanced Tutorials on Operational Research, 2015
Real features are all the additional characteristics an investor is interested to consider when s... more Real features are all the additional characteristics an investor is interested to consider when selecting a real portfolio, because they reflect preferences or information not captured by the model otherwise, or he/she is obliged to include as restrictions imposed by market conditions. Besides transaction costs, real features include, transaction lots, thresholds on investment, restriction on the number of assets (cardinality constraint), and decision dependency constraints among assets or classes of assets. In this chapter, we focus on all real features different from transaction costs. We analyze their practical relevance and show how to model them in a portfolio optimization problem. The modeling of some real features is possible by using as decision variables the asset shares. In several cases, however, the introduction of real features implies the need of variables that represent the amount of capital invested in each asset. When discussing each real feature, and the way to treat it in a portfolio optimization model, we specify if the use of amounts instead of shares is required. Finally, we show how the modeling of some real features may require the introduction of binary or integer variables giving rise to mixed integer linear programming problems.
EURO Advanced Tutorials on Operational Research, 2015
Annals of Operations Research, 2000
The original Markowitz model of portfolio selection has received a widespread theoretical accepta... more The original Markowitz model of portfolio selection has received a widespread theoretical acceptance and it has been the basis for various portfolio selection techniques. Nevertheless, this normative model has found relatively little application in practice when some additional features, such as fixed costs and minimum transaction lots, are relevant in the portfolio selection problem. In this paper different mixed-integer linear
European Journal of Operational Research, 1991
In this paper we describe a Decision Support System for dynamic job shop scheduling environments.... more In this paper we describe a Decision Support System for dynamic job shop scheduling environments. The supported decision situation includes several real-life features which are disregarded by conventional scheduling models. The system supports the planner in constructing efficient and effective schedules. The efficiency is guaranteed by algorithmic procedures and the effectiveness by interactive manipulation techniques. The due date achievement is the objective of the algorithmic support, but other objectives can be achieved by means of the control functions which allow the user to direct the decision process.
European Journal of Operational Research, 2014
Markowitz formulated the portfolio optimization problem through two criteria: the expected return... more Markowitz formulated the portfolio optimization problem through two criteria: the expected return and the risk, as a measure of the variability of the return. The classical Markowitz model uses the variance as the risk measure and is a quadratic programming problem. Many attempts have been made to linearize the portfolio optimization problem. Several different risk measures have been proposed which are computationally attractive as (for discrete random variables) they give rise to linear programming (LP) problems. About twenty years ago, the mean absolute deviation (MAD) model drew a lot of attention resulting in much research and speeding up development of other LP models. Further, the LP models based on the conditional value at risk (CVaR) have a great impact on new developments in portfolio optimization during the first decade of the 21st century. The LP solvability may become relevant for real-life decisions when portfolios have to meet side constraints and take into account transaction costs or when large size instances have to be solved. In this paper we review the variety of LP solvable portfolio optimization models presented in the literature, the real features that have been modeled and the solution approaches to the resulting models, in most of the cases mixed integer linear programming (MILP) models. We also discuss the impact of the inclusion of the real features.
RePEc: Research Papers in Economics, 2017
Multi-compartment vehicle routing problems arise in a variety of problem settings in which differ... more Multi-compartment vehicle routing problems arise in a variety of problem settings in which different product types have to be transported separated from each other. In this paper, a problem variant which occurs in the context of glass waste recycling is considered. In this problem, a set of locations exists, each of which offering a number of containers for the collection of different types of glass waste (e.g. colorless, green, brown glass). In order to pick up the contents from the containers, a fleet of homogeneous disposal vehicles is available. Individually for each disposal vehicle, the capacity can be discretely separated into a limited number of compartments to which different glass waste types are assigned. The objective of the problem is to minimize the total distance to be travelled by the disposal vehicles. For solving this problem to optimality, a branch-and-cut algorithm has been developed and implemented. Extensive numerical experiments have been conducted in order to evaluate the algorithm and to gain insights into the problem structure. The corresponding results show that the algorithm is able to solve instances with up to 50 locations to optimality and that it reduces the computing time by 87% compared to instances from the literature. Additional experiments give managerial insights into the use of different variants of compartments with flexible sizes.
Transportation Research Part C: Emerging Technologies
A massive use of electric vehicles is nowadays considered to be a key element of a sustainable tr... more A massive use of electric vehicles is nowadays considered to be a key element of a sustainable transportation policy and the availability of charging stations is a crucial issue for their extensive use. Charging stations in an urban area have to be deployed in such a way that they can satisfy a demand that may dramatically vary in space and time. In this paper we present an optimization model for the location of charging stations that takes into account the main specific features of the problem, in particular the different charging technologies, and their associated service time, and the fact that the demand depends on space and time. To measure the importance of incorporating the time dependence in an optimization model, we also present a simpler model that extends a classical location model and does not include the temporal dimension. A worst-case analysis and extensive computational experiments show that ignoring the temporal dimension of the problem may lead to a substantial amount of unsatisfied demand.
4OR, 2020
In Vehicle Routing Problems (VRPs) the decisions to be taken concern the assignment of customers ... more In Vehicle Routing Problems (VRPs) the decisions to be taken concern the assignment of customers to vehicles and the sequencing of the customers assigned to each vehicle. Additional decisions may need to be jointly taken, depending on the specific problem setting. In this paper, after discussing the different kinds of decisions taken in different classes of VRPs, the class where the decision about when the routes start from the depot has to be taken is considered and the related literature is reviewed. This class of problems, that we call VRPs over time, includes the periodic routing problems, the inventory routing problems, the vehicle routing problems with release dates, and the multi-trip vehicle routing problems.
Transportation Research Procedia, 2022
The class of inventory routing problems (IRP) includes a variety of different optimization prob-l... more The class of inventory routing problems (IRP) includes a variety of different optimization prob-lems that, though often very different from each other, all consider a routing and an inventory component of an optimization problem. Time may be discrete or continuous, demand may be deterministic or stochastic, inventory holding costs may be accounted for in the objective
EURO Journal on Decision Processes, 2019
In this paper, we analyze and discuss the optimization challenges and opportunities raised by the... more In this paper, we analyze and discuss the optimization challenges and opportunities raised by the decision of building an automated clinical laboratory in a hospital unit. We first describe the general decision setting from a strategic, tactical and operational perspective. We then focus on the analysis of a practical case, i.e., the Central Laboratory of a large urban academic teaching hospital in the North of Italy, the 'Spedali Civili' in Brescia. We will describe the present situation and the research opportunities related to the study of possible improvements of the management of the laboratory.
European Journal of Operational Research, 2018
Computers & Operations Research
Lecture Notes in Economics and Mathematical Systems, 2009
imply, even in the absence of a specific statement, that such names are exempt from the relevant ... more imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
European Journal of Operational Research, 1987
This paper proposes a discrete-time heterogeneous model to represent the interaction between the ... more This paper proposes a discrete-time heterogeneous model to represent the interaction between the dynamic arrival process of multiple TCP sources and a bottleneck queue. It utilises a novel time-variant calculation approach for transient queueing models, which modifies the conventional steady-state method by no longer requiring the equilibrium assumption. The main contributions are: (1) The limitation of the conventional queueing method is analysed and the benefits of the proposed modification is demonstrated; (2) The proposed dynamic arrival process of multiple sources is illustrated, which interacts with the queueing process and statistically responds to the positive and negative congestion feedback; (3) The fidelity of the proposed model is extensively validated by the closely matched results from MATLAB numerical solutions and NS-2 discrete-event simulation experiments.
Many cities and towns offer nowadays to citizens a bike sharing system (BSS). When a company star... more Many cities and towns offer nowadays to citizens a bike sharing system (BSS). When a company starts the service, several decisions have to be taken on the location and size of the rental stations, and the number of vehicles to use to re-balance the bikes in the stations, in addition to the cost and policies for the payment of the service. Also, when the service is in place, it is often necessary to modify it, in many cases to expand it. In this paper, starting from the experience gained in a real-case application, we present a simulation framework to support the tactical decisions in the design or revision of a BSS. We will also present the application of the framework to the case of Bicimia in Brescia, Italy.
European Journal of Operational Research, 2016
We consider a setting in which a company not only has a fleet of capacitated vehicles and drivers... more We consider a setting in which a company not only has a fleet of capacitated vehicles and drivers available to make deliveries, but may also use the services of occasional drivers who are willing to make a single delivery using their own vehicle in return for a small compensation if the delivery location is not too far from their own destination. The company seeks to make all the deliveries at minimum total cost, i.e., the cost associated with its own vehicles and drivers plus the compensation paid to the occasional drivers. The option to use occasional drivers to make deliveries gives rise to a new and interesting variant of the classical capacitated vehicle routing problem. We design and implement a multi-start heuristic which produces solutions with small errors when compared with optimal solutions obtained by solving an integer programming formulation with a commercial solver. A comprehensive computational study provides valuable insight into the potential of using occasional drivers to reduce delivery costs, focusing primarily on the number and flexibility of occasional drivers and the compensation scheme employed.
EURO Advanced Tutorials on Operational Research, 2015
Real features are all the additional characteristics an investor is interested to consider when s... more Real features are all the additional characteristics an investor is interested to consider when selecting a real portfolio, because they reflect preferences or information not captured by the model otherwise, or he/she is obliged to include as restrictions imposed by market conditions. Besides transaction costs, real features include, transaction lots, thresholds on investment, restriction on the number of assets (cardinality constraint), and decision dependency constraints among assets or classes of assets. In this chapter, we focus on all real features different from transaction costs. We analyze their practical relevance and show how to model them in a portfolio optimization problem. The modeling of some real features is possible by using as decision variables the asset shares. In several cases, however, the introduction of real features implies the need of variables that represent the amount of capital invested in each asset. When discussing each real feature, and the way to treat it in a portfolio optimization model, we specify if the use of amounts instead of shares is required. Finally, we show how the modeling of some real features may require the introduction of binary or integer variables giving rise to mixed integer linear programming problems.
EURO Advanced Tutorials on Operational Research, 2015
Annals of Operations Research, 2000
The original Markowitz model of portfolio selection has received a widespread theoretical accepta... more The original Markowitz model of portfolio selection has received a widespread theoretical acceptance and it has been the basis for various portfolio selection techniques. Nevertheless, this normative model has found relatively little application in practice when some additional features, such as fixed costs and minimum transaction lots, are relevant in the portfolio selection problem. In this paper different mixed-integer linear
European Journal of Operational Research, 1991
In this paper we describe a Decision Support System for dynamic job shop scheduling environments.... more In this paper we describe a Decision Support System for dynamic job shop scheduling environments. The supported decision situation includes several real-life features which are disregarded by conventional scheduling models. The system supports the planner in constructing efficient and effective schedules. The efficiency is guaranteed by algorithmic procedures and the effectiveness by interactive manipulation techniques. The due date achievement is the objective of the algorithmic support, but other objectives can be achieved by means of the control functions which allow the user to direct the decision process.
European Journal of Operational Research, 2014
Markowitz formulated the portfolio optimization problem through two criteria: the expected return... more Markowitz formulated the portfolio optimization problem through two criteria: the expected return and the risk, as a measure of the variability of the return. The classical Markowitz model uses the variance as the risk measure and is a quadratic programming problem. Many attempts have been made to linearize the portfolio optimization problem. Several different risk measures have been proposed which are computationally attractive as (for discrete random variables) they give rise to linear programming (LP) problems. About twenty years ago, the mean absolute deviation (MAD) model drew a lot of attention resulting in much research and speeding up development of other LP models. Further, the LP models based on the conditional value at risk (CVaR) have a great impact on new developments in portfolio optimization during the first decade of the 21st century. The LP solvability may become relevant for real-life decisions when portfolios have to meet side constraints and take into account transaction costs or when large size instances have to be solved. In this paper we review the variety of LP solvable portfolio optimization models presented in the literature, the real features that have been modeled and the solution approaches to the resulting models, in most of the cases mixed integer linear programming (MILP) models. We also discuss the impact of the inclusion of the real features.