Multi-objective Shortest Path Problem Research Articles

Labeling methods for partially ordered paths

The landscape of applications and subroutines relying on shortest path computations continues to grow steadily. This growth is driven by the undeniable success of shortest path algorithms in theory and practice. It also introduces new challenges as the models and assessing the optimality of paths become more complicated. Hence, multiple recent publications in the field adapt existing labeling methods in an ad hoc fashion to their specific problem variant without considering the underlying general structure: they always deal with multi-criteria scenarios, and those criteria define different partial orders on the paths. In this paper, we introduce the partial order shortest path problem (POSP), a generalization of the multi-objective shortest path problem (MOSP) and in turn also of the classical shortest path problem. POSP captures the particular structure of many shortest path applications as special cases. In this generality, we study optimality conditions or the lack of them, depending on the objective functions’ properties. Our final contribution is a big lookup table summarizing our findings and providing the reader with an easy way to choose among the most recent multi-criteria shortest path algorithms depending on their problems’ weight structure. Examples range from time-dependent shortest path bottleneck path problems to the electric vehicle shortest path problem with recharging and complex financial weight functions studied in the public transportation community. Our results hold for general digraphs and, therefore, surpass previous generalizations that were limited to acyclic graphs.

Enhanced Multi-Objective A* Using Balanced Binary Search Trees

This work addresses a Multi-Objective Shortest Path Problem (MO-SPP) on a graph where the goal is to find a set of Pareto-optimal solutions from a start node to a destination in the graph. A family of approaches based on MOA* have been developed to solve MO-SPP in the literature. Typically, these approaches maintain a "frontier" set at each node during the search process to keep track of the non-dominated, partial paths to reach that node. This search process becomes computationally expensive when the number of objectives increases as the number of Pareto-optimal solutions becomes large. In this work, we introduce a new method to efficiently maintain these frontiers for multiple objectives by incrementally constructing balanced binary search trees within the MOA* search framework. We first show that our approach correctly finds the Pareto-optimal front, and then provide extensive simulation results for problems with three, four and five objectives to show that our method runs faster than existing techniques by up to an order of magnitude.

An Efficient Label-Correcting Algorithm for the Multiobjective Shortest Path Problem

This paper proposes an exact algorithm to solve the one-to-one multiobjective shortest path problem. The solution involves determining a set of nondominated paths between two given nodes in a graph that minimizes several objective functions. This study is motivated by the application of this solution method to determine cycling itineraries. The proposed algorithm improves upon a label-correcting algorithm to rapidly solve the problem on large graphs (i.e., up to millions of nodes and edges). To verify the performance of the proposed algorithm, we use computational experiments to compare it with the best-known methods in the literature. The numerical results confirm the efficiency of the proposed algorithm. Summary of Contribution: The paper deals with a classic operations research problem (the one-to-one multiobjective shortest path problem) and is motivated by a real application for cycling itineraries. An efficient method is proposed and is based on a label-correcting algorithm into which several additional improvement techniques are integrated. Computational experiments compare this algorithm with the best-known methods in the literature to validate the performance on large-size graphs (Center for Discrete Mathematics and Theoretical Computer Science (DIMACS) instances from the ninth DIMACS challenge). New instances from the context of cycling itineraries are also proposed.

A Comparison of Genetic Representations and Initialisation Methods for the Multi-objective Shortest Path Problem on Multigraphs

This paper compares different solution approaches for the multi-objective shortest path problem (MSPP) on multigraphs. Multigraphs as a modelling tool are able to capture different available trade-offs between objectives for a given section of a route. For this reason, they are increasingly popular in modelling transportation problems with multiple conflicting objectives (e.g., travel time and fuel consumption), such as time-dependent vehicle routing, multi-modal transportation planning, energy-efficient driving, and airport operations. The multigraph MSPP is more complex than the NP-hard simple graph MSPP. Therefore, approximate solution methods are often needed to find a good approximation of the true Pareto front in a given time budget. Evolutionary algorithms have been successfully applied for the simple graph MSPP. However, there has been limited investigation of their applications to the multigraph MSPP. Here, we extend the most popular genetic representations to the multigraph case and compare the achieved solution qualities. Two heuristic initialisation methods are also considered to improve the convergence properties of the algorithms. The comparison is based on a diverse set of problem instances, including both bi-objective and triple objective problems. We found that the metaheuristic approach with heuristic initialisation provides good solutions in shorter running times compared to an exact algorithm. The representations were all found to be competitive. The results are encouraging for future application to the time-constrained multigraph MSPP.

An FPTAS for Dynamic Multiobjective Shortest Path Problems

The Dynamic Multiobjective Shortest Path problem features multidimensional costs that can depend on several variables and not only on time; this setting is motivated by flight planning applications and the routing of electric vehicles. We give an exact algorithm for the FIFO case and derive from it an FPTAS for both, the static Multiobjective Shortest Path (MOSP) problems and, under mild assumptions, for the dynamic problem variant. The resulting FPTAS is computationally efficient and beats the known complexity bounds of other FPTAS for MOSP problems.

Solving fuzzy multi-objective shortest path problem based on data envelopment analysis approach

The shortest path problem (SPP) is a special network structured linear programming problem that appears in a wide range of applications. Classical SPPs consider only one objective in the networks while some or all of the multiple, conflicting and incommensurate objectives such as optimization of cost, profit, time, distance, risk, and quality of service may arise together in real-world applications. These types of SPPs are known as the multi-objective shortest path problem (MOSPP) and can be solved with the existing various approaches. This paper develops a Data Envelopment Analysis (DEA)-based approach to solve the MOSPP with fuzzy parameters (FMOSPP) to account for real situations where input–output data include uncertainty of triangular membership form. This approach to make a connection between the MOSPP and DEA is more flexible to deal with real practical applications. To this end, each arc in a FMOSPP is considered as a decision-making unit with multiple fuzzy inputs and outputs. Then two fuzzy efficiency scores are obtained corresponding to each arc. These fuzzy efficiency scores are combined to define a unique fuzzy relative efficiency. Hence, the FMOSPP is converted into a single objective Fuzzy Shortest Path Problem (FSPP) that can be solved using existing FSPP algorithms.

Short and long term optimization for micro-object conveying with air-jet modular distributed system

Smart surface is a new conveying technology composed of a 2D planar surface presenting a matrix of distributed autonomous blocks. Every block contains a micro-electro-mechanical system (MEMS) actuator that controls the transfer of a possible object located above the block to the neighboring blocks, using air-jet forces. The spatial characteristics of the blocks impose some limits on the memory, energy and computation capabilities of the MEMS blocks. On the other hand, the system can reach several thousands of blocks making necessary to propose scalable algorithmic solutions.This paper studies different distributed algorithms to convey an object from an initial to a target position in the smart surface. The conveying policy emphasizes the long term use of the smart surface and the objects conveying efficiency measured by the time of the transfer. The problem stands as an original case of multi-objective Shortest Path problem (MOSP). Original because the quality of a given path is not evaluated by the sum of the weights of its segments, and because the segment weights change according to the used paths as provided by the algorithm itself. Therefore, the efficiency of a given algorithm is assessed on the basis of its performance during a long period of time.We describe here the best way to combine these two objectives and we propose a scalable incremental distributed protocol for objects conveying. The path optimality is adjusted according to the required calculation complexity. The performances of the different algorithmic and modeling variations are analyzed in terms of memory, time, computation and exchanged messages complexity. The obtained results prove the scalability of the algorithm, with linear computational, memory and convergence time complexity, and confirm the improvement of smart surface usage compared to a naive approach. The system lifespan increases of up to 130% on 40 × 40 smart surface, while the transfer cost (time and energy) is reduced. We show also that the computation time of the path with the incremental algorithm can be significantly reduced without significant degradation of the conveying system performance. For example, in a 40 × 40 smart surface, the number of messages is divided by 4 while the number of conveyed objects is only reduced by a ratio of 4%.

A Seismic Resistant Design Algorithm for Laying and Shielding of Optical Fiber Cables

This paper considers a long-haul optical fiber cable, connecting two points on the Earth's surface that passes through earthquake-prone or other sensitive areas. Different segments of the cable are characterized by different protection levels, where a higher level through shielding represents a more costly and more resilient segment. This leads to a multi-objective optimization problem, where the two objectives are 1) the total cost of the cable and 2) the total number of potential repairs along the cable likely to be caused by earthquakes. As a measure of seismic risk, we use the concept of cable repair rate used in the civil engineering community. In our models, ground motion intensity data are used to estimate the cable repair rate, and a graph of a triangulated irregular network is used to represent the Earth's surface. We formulate this optimization problem as a multi-objective shortest path problem and solve it by a variant of the label setting algorithm. Two approximate algorithms, an interval-partition-based label-setting algorithm and an evolutionary algorithm, are also presented as methods of computational cost reduction for large-scale cases, and their results are compared. The solution leads to a Pareto front or an approximate Pareto front that enables us to choose the path and protection of the cable to either minimize cost for a given risk level or minimize risk for a given budget.

An Approach for the Fast Calculation Method of Pareto Solutions of a Two-objective Network

The shortest path problem is a kind of optimization problem and its aim is to find the shortest path connecting two specific nodes in a network, where each edge has its distance. When considering not only the distances between the nodes but also some other information, the problem is formulated as a multi-objective shortest path problem that involves multiple conflicting objective functions. The multi-objective shortest path problem is a kind of optimization problem of multi-objective network. In the general cases, multi-objectives are rarely optimized by a solution. So, to solve the multi-objective shortest path problem leads to obtaining Pareto solutions. An algorithm for this problem has been proposed by using the extended Dijkstra's algorithm. However, this algorithm for obtaining Pareto solutions has many useless searches for paths. In this study, we consider two-objective shortest path problem and propose efficient algorithms for obtaining the Pareto solutions. Our proposed algorithm can reduce more search space than existing algorithms, by solving a single-objective shortest path problem. The results of the numerical experiments suggest that our proposed algorithms reduce the computing time and the memory size for obtaining the Pareto solutions.

Solution approaches for determining user-oriented paths on dynamic networks

This paper addresses the time dependent multi-objective constrained shortest path problem. Solving the problem aims at providing the user a Pareto-optimal solution associated with an efficient path. The solution process takes into account information given by the user in order to obtain a path, satisfying his/her requirements. For the first time, more than two criteria are considered and the reference point methodology is used to define the aggregation function. In addition, knapsack-like constraints are introduced in the formulation in order to model budget restrictions. Dynamic-programming-based algorithms are devised and tested on randomly generated networks and on real life instances derived from US city maps. The computational results underline that the proposed algorithms are able to solve the problem in a reasonable amount of time. This is a good result since the problem considered contains features of three NP-hard problems: the multi-objective, the constrained and the time dependent shortest path problems.

Finding highly preferred points for multi-objective integer programs

This article develops exact algorithms to generate all non-dominated points in a specified region of the criteria space in Multi-Objective Integer Programs (MOIPs). Typically, there are too many non-dominated points in large MOIPs and it is not practical to generate them all. Therefore, the problem of generating non-dominated points in the preferred region of the decision-maker is addressed. To define the preferred region, the non-dominated set is approximated using a hyper-surface. A procedure is developed that then finds a preferred hypothetical point on this surface and defines a preferred region around the hypothetical point. Once the preferred region is defined, all non-dominated points in that region are generated. The performance of the proposed approach is tested on multi-objective assignment, multi-objective knapsack, and multi-objective shortest path problems with three and four objectives. Computational results show that a small set of non-dominated points is generated that contains highly preferred points in a reasonable time.

Multiobjective shortest path problems with lexicographic goal-based preferences

Multiobjective shortest path problems are computationally harder than single objective ones. In particular, execution time is an important limiting factor in exact multiobjective search algorithms. This paper explores the possibility of improving search performance in those cases where the interesting portion of the Pareto front can be initially bounded. We introduce a new exact label-setting algorithm that returns the subset of Pareto optimal paths that satisfy a set of lexicographic goals, or the subset that minimizes deviation from goals if these cannot be fully satisfied. Formal proofs on the correctness of the algorithm are provided. We also show that the algorithm always explores a subset of the labels explored by a full Pareto search. The algorithm is evaluated over a set of problems with three objectives, showing a performance improvement of up to several orders of magnitude as goals become more restrictive.

A Fine-Grained Clock Buffer Polarity Assignment for High-Speed and Low-Power Digital Systems

The clock buffer polarity assignment is one of the effective design schemes to mitigate the power/ground noise caused by the clock signal propagation in high-speed digital systems. This paper overcomes a set of fundamental limitations of the conventional clock buffer polarity assignment methods, which are: 1) the unawareness of the signal delay (i.e., arrival time) differences to the leaf clock buffering elements; 2) the ignorance of the effect of the current fluctuation of nonleaf clock buffering elements on the total peak current waveform; and 3) the inability of supporting low-power digital designs with multiple (dynamically operating) power modes. Clearly, not addressing 1 and 2 in the polarity assignment may cause a severe inaccuracy on the peak current estimation, which results in unnecessarily high peak current. Moreover, without tackling 3, designs may suffer from clock skew violation in some of the power modes, affecting circuit speed or reliability. To overcome the limitations, we propose a completely new fine-grained approach to the clock buffer polarity assignment combined with buffer sizing, formulating the problem into a multiobjective shortest path problem and solving it effectively for designs with a single power mode, while exploiting the flexibility of our multiobjective shortest path formulation for designs with multiple power modes. Through experiments using benchmark circuits, it is shown that the proposed approach is able to produce designs with 17% lower peak current and 20% lower power noise on average, compared with the results produced by the best ever known method.

A memory efficient stochastic evolution based algorithm for the multi-objective shortest path problem

Multi-objective shortest path (MOSP) problem aims to find the shortest path between a pair of source and a destination nodes in a network. This paper presents a stochastic evolution (StocE) algorithm for solving the MOSP problem. The proposed algorithm is a single-solution-based evolutionary algorithm (EA) with an archive for storing several non-dominant solutions. The solution quality of the proposed algorithm is comparable to the established population-based EAs. In StocE, the solution replaces its bad characteristics as the generations evolve. In the proposed algorithm, different sub-paths are the characteristics of the solution. Using the proposed perturb operation, it eliminates the bad sub-paths from generation to generation. The experiments were conducted on huge real road networks. The proposed algorithm is comparable to well-known single-solution and population-based EAs. The single-solution-based EAs are memory efficient, whereas, the population-based EAs are known for their good solution quality. The performance measures were the solution quality, speed and memory consumption, assessed by the hypervolume (HV) metric, total number of evaluations and memory requirements in megabytes. The HV metric of the proposed algorithm is superior to that of the existing single-solution and population-based EAs. The memory requirements of the proposed algorithm is at least half than the EAs delivering similar solution quality. The proposed algorithms also executes more rapidly than the existing single-solution-based algorithms. The experimental results show that the proposed algorithm is suitable for solving MOSP problems in embedded systems.

Parametric search and problem decomposition for approximating Pareto-optimal paths

The multiobjective shortest path problem arises in many transportation and logistics applications, either as a stand-alone network routing problem or a subroutine of a more complex multiobjective network optimization problem. It has been addressed by different solution strategies, including labeling methods, ranking methods, constraint methods, and parametric methods. Increasing attention has been paid to parametric methods in recent years, partially because of its simple algorithmic logic and its flexibility of being used in different user-preference decision-making environments. The core idea of a parametric algorithm is scalarization, by which a multiobjective shortest path problem can be tackled by repeatedly solving a single-objective subproblem. However, existing parametric algorithms suffer two notorious deficiencies, which considerably limit its further applications: first, typical subroutines for the single-objective subproblem in general cannot capture nonextreme Pareto-optimal paths; second, parametric algorithms for biobjective problems cannot be directly extended to solving multiobjective problems. This paper provides some algorithmic improvements that can partially overcome these deficiencies. In particular, the contribution of this work is twofold: first, in the biobjective parametric solution framework, we propose an approximate label-setting algorithm for the parameterized, constrained single-objective subproblem, which is capable of identifying all extreme paths and a large percentage (i.e., 85–100%) of nonextreme paths; second, we suggest a general projection scheme that can decompose a multiobjective problem into a number of biobjective problems. The approximate parametric algorithm runs in polynomial time. The algorithmic design and solution performance of the algorithm for multiobjective shortest path problems are illustrated, and numerically evaluated and compared with a benchmark algorithm in terms of solution completeness and efficiency.

Analyzing the impact of MOACO components: An algorithmic study on the multi-objective shortest path problem

Multi-objective Ant Colony Optimization (MOACO) algorithms have been successfully applied to several multi-objective combinatorial optimization problems (MCOP) over the past decade. Recently, we proposed a MOACO algorithm named GRACE for the multi-objective shortest path (MSP) problem, confirming the efficiency of such metaheuristic for this MCOP. In this paper, we investigate several extensions of GRACE, proposing several single and multi-colony variants of the original algorithm. All variants are compared on the original set of instances used for proposing GRACE. The best-performing variants are also assessed using a new benchmark containing 300 larger instances with three different underlying graph structures. Experimental evaluation shows one of the variants to produce better results than the others, including the original GRACE, thus improving the state-of-the-art of MSP.

A Fast Calculation Method for the Partial Group of All Pareto Solutions at a Three-Objective Network

The multi-objective network model can be applied to common problems with many conditions, for example, optimal routing of a network connection to the Internet services, optimally scheduling of a production and distribution systems, and multistage-structured modeling for supply chain management systems, etc. The shortest path problem is an optimization problem for finding the shortest path connecting two specific nodes of a directed or undirected graph. When considering not only the distances between the nodes but also other information, for example, toll, fuel cost, or gradient, the problem is formulated as a multi-objective shortest path problem that involves multiple conflicting objective functions. To solve the optimization problem of multi-objective network is difficult because the multiple objectives have to be simultaneously optimized. Thus, few algorithms for this problem have been proposed. In this study, we use a three-objective shortest path problem to find the shortest path between two terminal nodes on a network, and we propose three efficient algorithms for obtaining the Pareto solutions based on the extended Dijkstra’s algorithm. We use our algorithms to find the partial group of all Pareto solutions. The results of the numerical experiments suggest that the proposed algorithms reduce the computing time and the memory size for obtaining the Pareto solutions. In addition, we show the algorithms could find almost set of solution in the Pareto solutions.

An Interactive Algorithm for Multi-objective Route Planning

We address the route selection problem for Unmanned Air Vehicles (UAV) under multiple objectives. We consider a general case for this problem, where the UAV has to visit several targets and return to the base. We model this problem as a combination of two combinatorial problems. First, the path to be followed between each pair of targets should be determined. We model this as a multi-objective shortest path problem. Additionally, we need to determine the order of the targets to be visited. We model this as a multi-objective traveling salesperson problem (MOTSP). The overall problem is a combination of these two problems, which we define as a generalized MOTSP. We develop an exact interactive approach to identify the best paths and the best tour of a decision maker under a linear utility function.

Editorial for the Special Issue on Theoretical Aspects of Evolutionary Multi-Objective Optimization

Evolutionary algorithms have been widely used to tackle multi-objective optimization problems. Despite many successful applications there is a lack of theoretical knowledge on how and why this type of algorithm works particularly well for multi-objective problems. This special issue presents current advances to the theoretical understanding of evolutionary algorithms for multi-objective optimization. It comprises four very high quality papers which have been selected via a rigorous reviewing process. The first paper “On the Effect of Populations in Evolutionary Multi-Objective Optimisation” by Oliver Giel and Per Kristian Lehre studies the basic question whether a population is provably useful to compute the whole Pareto front of a multi-objective optimization problem. They compare restart strategies of several single-objective approaches based on one individual to a natural multi-objective approach using a population. Their analyses point out the benefits of the multi-objective evolutionary algorithm in a rigorous way. Using illustrative example functions they provide not only proven results but also a good intuition about why population-based approaches can outperform individual-based approaches in multi-objective optimization. The paper “Exploring the Runtime of an Evolutionary Algorithm for the Multi-Objective Shortest Path Problem” by Christian Horoba examines the behavior of evolutionary algorithms for the classical NP-hard multi-objective shortest path problem. The author considers an evolutionary approach based on -dominance and proves that this algorithm constitutes a fully polynomial-time randomized approximation scheme (FPRAS) for the problem. The algorithm achieves this by mimicking a problemspecific algorithm for that problem. This provides general insight into why evolutionary algorithms can perform well for problems that allow for efficient problem-specific algorithms. Hypervolume-based algorithms have become very popular in evolutionary multiobjective optimization. In the paper, “An Efficient Algorithm for Computing Hypervolume Contributions,” Karl Bringmann and Tobias Friedrich present a faster algorithm for determining the individual with the smallest hypervolume contribution in a given population. Furthermore, they study the problem of removing λ > 1 individuals with the smallest hypervolume contribution from a given population and present an elegant and fast method to carry out this task.

Search for the best compromise solution on Multiobjective shortest path problem

Abstract This paper deals with the multiobjective shortest path problem in the context of routing for cycling. Many studies focus on the computation of the entire set of Pareto paths. Here we focus on the determination of a well-balanced trade-off path between the objectives. We recall the original Best Compromise A* method and then we present two improvements in order to speed up the search of the best compromise solution. Finally we present various numerical tests on real-life instances, that prove the efficiency of the improved methods.