A customized multi-objective evolutionary algorithm (MOEA) is proposed for the flexible job shop scheduling problem (FJSP) with three objectives: makespan, total workload, critical workload. In... Show moreA customized multi-objective evolutionary algorithm (MOEA) is proposed for the flexible job shop scheduling problem (FJSP) with three objectives: makespan, total workload, critical workload. In general, the algorithm can be integrated with any standard MOEA. In this paper, it has been combined with NSGA-III to solve the state-of-the-art benchmark FJSPs, whereas an off-the-shelf implementation of NSGA-III is not capable of solving them. Most importantly, we use the various algorithm adaptations to enhance the performance of our algorithm. To be specific, it uses smart initialization approaches to enrich the first-generation population, and proposes new crossover operator to create a better diversity on the Pareto front approximation. The MIP-EGO configurator is adopted to automatically tune the mutation probabilities, which are important hyper-parameters of the algorithm. Furthermore, different local search strategies are employed to explore the neighborhood for better solutions. The experimental results from the combination of these techniques show the good performance as compared to classical evolutionary scheduling algorithms and it requires less computing budget. Even some previously unknown non-dominated solutions for the BRdata benchmark problems could be discovered. Show less
Rios, T.; Kong, J.; Stein, B. van; Bäck, T.H.W.; Wollstadt, P.; Sendhoff, B.; Menzel, S. 2020
Point cloud autoencoders were recently introduced as powerful models for data compression. They learn a lowdimensional set of variables that are suitable as design parameters for shape generation... Show morePoint cloud autoencoders were recently introduced as powerful models for data compression. They learn a lowdimensional set of variables that are suitable as design parameters for shape generation and optimization problems. In engineering tasks, 3D point clouds are often derived from fine polygon meshes, which are the most suitable representations for physics simulation, e.g., computational fluid dynamics (CFD). Yet, the reconstruction of high-quality meshes from autoencoder-based point clouds is challenging, often requiring supervised and manual work, which is prohibitive during the optimization. Target shape matching optimization using existing mesh prototypes overcomes the difficulties of recovering shape information from the point coordinates. However, for autoencoders trained on data sets comprising shapes with high degree of dissimilarity, there is not a single mesh prototype that can fit any autoencoder-based point cloud, and the selection of a set of prototypes is nontrivial. In the present paper we propose a method for optimizing a selection of prototypical meshes to match the maximum number of shapes in the autoencoder output space as possible, which is achieved by linking the advantages of the latent space representation of an autoencoder and the state-of-the-art free form deformation (FFD) method. Furthermore, we approached the balance between costs (number of mesh prototypes) and number of covered shapes by varying the number of prototypes and the dimensionality of the autoencoder latent space, showing that higher-dimensional latent spaces encode finer geometric changes, requiring more sophisticated FFD setups. Show less
