415 research outputs found
Peeking beyond peaks:Challenges and research potentials of continuous multimodal multi-objective optimization
Multi-objective (MO) optimization, i.e., the simultaneous optimization of multiple conflicting objectives, is gaining more and more attention in various research areas, such as evolutionary computation, machine learning (e.g., (hyper-)parameter optimization), or logistics (e.g., vehicle routing). Many works in this domain mention the structural problem property of multimodality as a challenge from two classical perspectives: (1) finding all globally optimal solution sets, and (2) avoiding to get trapped in local optima. Interestingly, these streams seem to transfer many traditional concepts of single-objective (SO) optimization into claims, assumptions, or even terminology regarding the MO domain, but mostly neglect the understanding of the structural properties as well as the algorithmic search behavior on a problem's landscape. However, some recent works counteract this trend, by investigating the fundamentals and characteristics of MO problems using new visualization techniques and gaining surprising insights. Using these visual insights, this work proposes a step towards a unified terminology to capture multimodality and locality in a broader way than it is usually done. This enables us to investigate current research activities in multimodal continuous MO optimization and to highlight new implications and promising research directions for the design of benchmark suites, the discovery of MO landscape features, the development of new MO (or even SO) optimization algorithms, and performance indicators. For all these topics, we provide a review of ideas and methods but also an outlook on future challenges, research potential and perspectives that result from recent developments.</p
Scalable and customizable benchmark problems for many-objective optimization
Solving many-objective problems (MaOPs) is still a significant challenge in the multi-objective optimization (MOO) field. One way to measure algorithm performance is through the use of benchmark functions (also called test functions or test suites), which are artificial problems with a well-defined mathematical formulation, known solutions and a variety of features and difficulties. In this paper we propose a parameterized generator of scalable and customizable benchmark problems for MaOPs. It is able to generate problems that reproduce features present in other benchmarks and also problems with some new features. We propose here the concept of generative benchmarking, in which one can generate an infinite number of MOO problems, by varying parameters that control specific features that the problem should have: scalability in the number of variables and objectives, bias, deceptiveness, multimodality, robust and non-robust solutions, shape of the Pareto front, and constraints. The proposed Generalized Position-Distance (GPD) tunable benchmark generator uses the position-distance paradigm, a basic approach to building test functions, used in other benchmarks such as Deb, Thiele, Laumanns and Zitzler (DTLZ), Walking Fish Group (WFG) and others. It includes scalable problems in any number of variables and objectives and it presents Pareto fronts with different characteristics. The resulting functions are easy to understand and visualize, easy to implement, fast to compute and their Pareto optimal solutions are known.This work has been supported by the Brazilian agencies (i) National Council for Scientific and Technological Development (CNPq); (ii) Coordination for the Improvement of Higher Education (CAPES) and (iii) Foundation for Research of the State of Minas Gerais (FAPEMIG, in Portuguese)
One PLOT to Show Them All: Visualization of Efficient Sets in Multi-Objective Landscapes
Visualization techniques for the decision space of continuous multi-objective
optimization problems (MOPs) are rather scarce in research. For long, all
techniques focused on global optimality and even for the few available
landscape visualizations, e.g., cost landscapes, globality is the main
criterion. In contrast, the recently proposed gradient field heatmaps (GFHs)
emphasize the location and attraction basins of local efficient sets, but
ignore the relation of sets in terms of solution quality.
In this paper, we propose a new and hybrid visualization technique, which
combines the advantages of both approaches in order to represent local and
global optimality together within a single visualization. Therefore, we build
on the GFH approach but apply a new technique for approximating the location of
locally efficient points and using the divergence of the multi-objective
gradient vector field as a robust second-order condition. Then, the relative
dominance relationship of the determined locally efficient points is used to
visualize the complete landscape of the MOP. Augmented by information on the
basins of attraction, this Plot of Landscapes with Optimal Trade-offs (PLOT)
becomes one of the most informative multi-objective landscape visualization
techniques available.Comment: This version has been accepted for publication at the 16th
International Conference on Parallel Problem Solving from Nature (PPSN XVI
Explicitly Multi-Modal Benchmarks for Multi-Objective Optimization
In multi-objective optimization, designing good benchmark problems is an
important issue for improving solvers. Although many benchmark problems have
been proposed and some of them became de facto standards, designing multimodal
problems that have a controllable landscape is still an open problem especially
for high-dimensional cases. We thus propose the Benchmark with Explicit
Multimodality (BEM), which lets the benchmark designer specify the basins of
attraction using a graph structure known as the reachability graph. In this
article, we focus on the mathematical formulation of the BEM. We will see that
the BEM has preferable characteristics such as (i) realizing user-specified
local Pareto set, (ii) allowing high-dimensional design spaces and (iii)
possessing nonseparability
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