The multi-path Traveling Salesman Problem with stochastic travel costs

Given a set of nodes, where each pair of nodes is connected by several paths and each path shows a stochastic travel cost with unknown probability distribution, the multi-path Traveling Salesman Problem with stochastic travel costs aims at finding an expected minimum Hamiltonian tour connecting all nodes. Under a mild assumption on the unknown probability distribution, a deterministic approximation of the stochastic problem is given. The comparison of such approximation with a Monte Carlo simulation shows both the accuracy and the efficiency of the deterministic approximation, with a mean percentage gap around 2% and a reduction of the computational times of two orders of magnitude

The multi-stage dynamic stochastic decision process with unknown distribution of the random utilities

We consider a decision maker who performs a stochastic decision process over a multiple number of stages, where the choice alternatives are characterized by random utilities with unknown probability distribution. The decisions are nested each other, i.e. the decision taken at each stage is affected by the subsequent stage decisions. The problem consists in maximizing the total expected utility of the overall multi-stage stochastic dynamic decision process. By means of some results of the extreme values theory, the probability distribution of the total maximum utility is derived and its expected value is found. This value is proportional to the logarithm of the accessibility of the decision maker to the overall set of alternatives in the different stages at the start of the decision process. It is also shown that the choice probability to select alternatives becomes a Nested Multinomial Logit model

How to locate services optimizing redundancy: A comparative analysis of K-Covering Facility Location models

Redundancy aspects related to covering facility location problems are of extreme importance for many applications, in particular those regarding critical services. For example, in the healthcare sector, facilities such as ambulances or first-aid centers must be located robustly against unpredictable events causing disruption or congestion. In this paper, we propose different modeling tools that explicitly address coverage redundancy for the underlying service. We also evaluate, both theoretically and experimentally, the properties and behavior of the models, and compare them from a computational and managerial point of view. More precisely, by starting from three classical double-covering models from the literature (BACOP1, BACOP2, and DSM), we define three parametric families of models (namely, K-BACOP1, K-BACOP2, and K-DSM) which generalize the former to any possible Kth coverage level of interest. The study of such generalizations allows us to derive interesting managerial insights on location decisions at the strategic level. The CPU performance and the quality of the solutions returned are assessed through ad-hoc KPIs collected over many representative instances with different sizes and topological characteristics, and also by dynamically simulating scenarios involving possible disruption for the located facilities. Finally, a real case study concerning ambulance service in Morocco is analyzed. The results show that, in general, K-BACOP1 performs very well, even if intrinsic feasibility issues limit its broad applicability. Instead, K-DSM achieves the best coverage and equity performances for lower levels of redundancy, while K-BACOP2 seems the most robust choice when high redundancy is required, showing smoother and more predictable trends

The synchronized multi-commodity multi-service Transshipment-Hub Location Problem with cyclic schedules

The synchronized multi-commodity multi-service Transshipment-Hub Location Problem is a hub location problem variant faced by a logistics service provider operating in the context of synchromodal logistics. The provider must decide where and when to locate transshipment facilities in order to manage many customers’ origin–destination shipments with release and due dates while minimizing a total cost given by location costs, transportation costs, and penalties related to unmet time constraints. The considered synchromodal network involves different transportation modes (e.g., truck, rail, river and sea navigation) to perform long-haul shipments and the freight synchronization at facilities for transshipment operations. To the best of our knowledge, this variant has never been studied before. Considering a time horizon in which both transportation services and demand follow a cyclic pattern, we propose a time–space network representation of the problem and an ad-hoc embedding of the time-dependent parameters into the network topology and the arcs’ weight. This allows to model the flow synchronization required by the problem through a Mixed-Integer Linear Programming formulation with a simplified structure, similar to well-known hub location problems and avoiding complicating constraints for managing the time dimension. Through an extensive experimental campaign conducted over a large set of realistic instances, we present a computational and an economic analysis. In particular, we want to assess the potential benefits of implementing synchromodal logistics operations into long-haul supply-chains managed by large service providers. Since flexibility is one of the main features of synchromodality, we evaluate the impact on decisions and costs of different levels of flexibility regarding terminals’ operations and customers’ requirements

Heuristics for the two-echelon vehicle routing problem: A multi-start approach

Tech. Rep. CIRRELT-2011-16, CIRRELT, Montreal, Canad

The Two-Echelon Capacitated Vehicle Routing Problem

Multi-echelon distribution systems are quite common in supply-chain and logistic systems. They are used by public administrations in their transportation and traffic planning strategies as well as by companies to model their distribution systems. Unfortunately, the literature on com- binatorial optimization methods for multi-echelon distribution systems is very poor. The aim of this paper is twofold. Firstly, it introduces the family of Multi-Echelon Vehicle Routing Problems. Second, the Two-Echelon Capacitated Vehicle Routing Problem, is presented. The Two-Echelon Capacitated Vehicle Routing Problem (2E-CVRP) is an extension of the classical VRP where the delivery passes through intermediate depots (called satellites). As in the classical VRP, the goal is to deliver goods to customers with known demands, minimizing the total delivery cost while considering vehicle and satellites capacity constraints. A mathematical model for 2E-CVRP is presented and some valid in- equalities given, which are able to significantly improve the results on benchmark tests up to 50 customers and 5 satellites. Computational re- sults under different realistic scenarios are presented

A greedy adaptive search procedure for multi-dimensional multi-container packing problems

Tech. Rep. CIRRELT-2012-10, CIRRELT, Montrea

Geographical Anaylsis of Landscape in the Wat Chan Watershed, Northern Thailand

Deforestation, one of the important problems in the tropical forest, can affect the accelerated land degradation that lead to decreased soil productivity and agricultural production. Geographical attributes in the landscape, such as land use types, topographic attributes, and soil information play important roles in determining the landscape structure and functions. This study used spatial analysis, such as GIS overlay and a non-parametric test of land use dynamics to provide a historic documents of deforestation and land use dynamics in the Wat Chan watershed, between 1974 and 1996. Soil-landscape relationships were used to express our understanding of the distribution of soil materials in relation to geomorphologic features. The method of a non-parametric trend analysis for land use change permits extracting a probability of change in land use and helps illustrate that about 0.76% of the landscape can be identified as cycled land. Regressing the probability of land use change on physical attributes and topographic attributes indicated that increased land use change from forest to open lands were associated with short distances to villages, short distances to forest edge, high elevation and high CTI (R^ = 0.74). Analysis of soil landscape indicated that elevation, slope, land use, and annual rainfall were the attributes most highly correlated with measured soil properties. CTI and profile curvature showed some influence on the variation of N and OM in this landscape. Coefficients of sand, silt, N, OM, extractable P, and bulk density variable were highly significant as indicated by t-test with R^ ranged from 0.40 to 0.55. Multiple criteria analysis was used to characterize degradation of sub-watersheds based on landscape attributes that are influencing erosion. Only two sub-watersheds were characterized as extremely low degradation while five sub-watersheds were characterized as high degradation. The most of sub-watershed were classified as low and moderately degraded. Results illustrate that spatial analysis and GIS can improve understanding of geographical distribution in the Wat Chan watershed in both spatial and temporal aspects. This knowledge of landscape attributes and their spatial and temporal variation are important components for efficient management of resources in the Wat Chan watershed, Northern Thailand

Nested Dynamics of Metropolitan Processes and Policies: Turin

BACKGROUND PAPERS FOR THE METROPOLITAN STUDY: 3 -- The project "Nested Dynamics of Metropolitan Processes and Policies" was initiated by the Regional and urban Development Group at IIASA in 1983 and work on this collaborative study started the same year. This Series of contributions represents "entry tickets" to the Project, i.e., initial statements by authors from individual metropolitan regions that are participating in the Project's network. The aim of these papers is threefold. First, to provide some background information describing the processes of change within four principal subsystems: population, housing, economy, and transportation. Second, to identify major trends and crucial policy issues which are to constitute a focus for the subsequent analytical and modeling work. Third, to facilitate comparative studies of development paths among these regions and the dynamic interdependencies between the above subsystems. The background information contained in this paper pertains to the Turin metropolitan region