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Niki van Stein

Associate Professor in Explainable AI for ML and Optimization at LIACS, Leiden University.

XAI group

The Explainable AI research group at LIACS, Leiden University: making complex systems understandable enough to trust.

Posts

Our new book: Agentic Large Language Models

3 minute read

Published:

After a year and a half of writing, our textbook on agentic LLMs is out as a preprint, with a Springer edition and a new master course to go with it.

projects

CIMPLO

Cross-Industry Predictive Maintenance Optimization Platform

XAIPre

eXplainable AI for Predictive Maintenance

LLaMEA

Large Language Evolutionary Algorithm for the automatic design of algorithms.

AI4optics

AI-based simulation, design and reconstruction for illumination and imaging optics.

FIND

Large AI models for a resilient high-tech industry.

GenAIDE

Exploring disruptive AI technologies and evolving computer-aided engineering.

publications

Fitness landscape analysis of nk landscapes and vehicle routing problems by expanded barrier trees

Published in EVOLVE-A Bridge between Probability, Set Oriented Numerics, and Evolutionary Computation IV: International Conference held at Leiden University, July 10-13, 2013, 2013

Recommended citation: Niki van Stein, Michael Emmerich, Zhiwei Yang, "Fitness landscape analysis of nk landscapes and vehicle routing problems by expanded barrier trees." EVOLVE-A Bridge between Probability, Set Oriented Numerics, and Evolutionary Computation IV: International Conference held at Leiden University, July 10-13, 2013, 2013. https://doi.org/10.1007/978-3-319-01128-8_6

Optimally weighted cluster kriging for big data regression

Published in Advances in Intelligent Data Analysis XIV: 14th International Symposium, IDA 2015, Saint Etienne. France, October 22-24, 2015. Proceedings, 2015

Recommended citation: Niki van Stein, Hao Wang, Wojtek Kowalczyk, Thomas Bäck, Michael Emmerich, "Optimally weighted cluster kriging for big data regression." Advances in Intelligent Data Analysis XIV: 14th International Symposium, IDA 2015, Saint Etienne. France, October 22-24, 2015. Proceedings, 2015. https://doi.org/10.1007/978-3-319-24465-5_27

An incremental algorithm for repairing training sets with missing values

Published in Information Processing and Management of Uncertainty in Knowledge-Based Systems: 16th International Conference, IPMU 2016, Eindhoven, The Netherlands, June 20-24, 2016, Proceedings, Part II 16, 2016

Recommended citation: Niki van Stein, Wojtek Kowalczyk, "An incremental algorithm for repairing training sets with missing values." Information Processing and Management of Uncertainty in Knowledge-Based Systems: 16th International Conference, IPMU 2016, Eindhoven, The Netherlands, June 20-24, 2016, Proceedings, Part II 16, 2016. https://doi.org/10.1007/978-3-319-40581-0_15

Analysis and visualization of missing value patterns

Published in Information Processing and Management of Uncertainty in Knowledge-Based Systems: 16th International Conference, IPMU 2016, Eindhoven, The Netherlands, June 20-24, 2016, Proceedings, Part II 16, 2016

Recommended citation: Niki van Stein, Wojtek Kowalczyk, Thomas Bäck, "Analysis and visualization of missing value patterns." Information Processing and Management of Uncertainty in Knowledge-Based Systems: 16th International Conference, IPMU 2016, Eindhoven, The Netherlands, June 20-24, 2016, Proceedings, Part II 16, 2016. https://doi.org/10.1007/978-3-319-40581-0_16

Towards data driven process control in manufacturing car body parts

Published in 2016 International Conference on Computational Science and Computational Intelligence (CSCI), 2016

Recommended citation: Niki van Stein, Matthijs Van Leeuwen, Hao Wang, Stephan Purr, Sebastian Kreissl, Josef Meinhardt, Thomas Bäck, "Towards data driven process control in manufacturing car body parts." 2016 International Conference on Computational Science and Computational Intelligence (CSCI), 2016. https://doi.org/10.1109/csci.2016.0093

A novel uncertainty quantification method for efficient global optimization

Published in Information Processing and Management of Uncertainty in Knowledge-Based Systems. Applications: 17th International Conference, IPMU 2018, C'adiz, Spain, June 11-15, 2018, Proceedings, Part III 17, 2018

Recommended citation: Niki van Stein, Hao Wang, Wojtek Kowalczyk, Thomas Bäck, "A novel uncertainty quantification method for efficient global optimization." Information Processing and Management of Uncertainty in Knowledge-Based Systems. Applications: 17th International Conference, IPMU 2018, C'adiz, Spain, June 11-15, 2018, Proceedings, Part III 17, 2018. https://doi.org/10.1007/978-3-319-91479-4_40

Designing ships using constrained multi-objective efficient global optimization

Published in Machine Learning, Optimization, and Data Science: 4th International Conference, LOD 2018, Volterra, Italy, September 13-16, 2018, Revised Selected Papers 4, 2019

Recommended citation: Roy de Winter, Niki van Stein, Matthys Dijkman, Thomas Bäck, "Designing ships using constrained multi-objective efficient global optimization." Machine Learning, Optimization, and Data Science: 4th International Conference, LOD 2018, Volterra, Italy, September 13-16, 2018, Revised Selected Papers 4, 2019. https://doi.org/10.1007/978-3-030-13709-0_16

On the efficiency of a point cloud autoencoder as a geometric representation for shape optimization

Published in 2019 IEEE Symposium Series on Computational Intelligence (SSCI), 2019

Recommended citation: Thiago Rios, Bernhard Sendhoff, Stefan Menzel, Thomas Bäck, Niki van Stein, "On the efficiency of a point cloud autoencoder as a geometric representation for shape optimization." 2019 IEEE Symposium Series on Computational Intelligence (SSCI), 2019. https://doi.org/10.1109/ssci44817.2019.9003161

Improving NSGA-III for flexible job shop scheduling using automatic configuration, smart initialization and local search

Published in Proceedings of the 2020 Genetic and Evolutionary Computation Conference Companion, 2020

Recommended citation: Yali Wang, Niki van Stein, Thomas Bäck, Michael Emmerich, "Improving NSGA-III for flexible job shop scheduling using automatic configuration, smart initialization and local search." Proceedings of the 2020 Genetic and Evolutionary Computation Conference Companion, 2020. https://doi.org/10.1145/3377929.3389924

Back to meshes: Optimal simulation-ready mesh prototypes for autoencoder-based 3D car point clouds

Published in 2020 IEEE Symposium Series on Computational Intelligence (SSCI), 2020

Recommended citation: Thiago Rios, Jiawen Kong, Niki van Stein, Thomas Bäck, Patricia Wollstadt, Bernhard Sendhoff, Stefan Menzel, "Back to meshes: Optimal simulation-ready mesh prototypes for autoencoder-based 3D car point clouds." 2020 IEEE Symposium Series on Computational Intelligence (SSCI), 2020. https://doi.org/10.1109/ssci47803.2020.9308400

Samo-cobra: A fast surrogate assisted constrained multi-objective optimization algorithm

Published in Evolutionary Multi-Criterion Optimization: 11th International Conference, EMO 2021, Shenzhen, China, March 28--31, 2021, Proceedings 11, 2021

Recommended citation: Roy de Winter, Niki van Stein, Thomas Bäck, "Samo-cobra: A fast surrogate assisted constrained multi-objective optimization algorithm." Evolutionary Multi-Criterion Optimization: 11th International Conference, EMO 2021, Shenzhen, China, March 28--31, 2021, Proceedings 11, 2021. https://doi.org/10.1007/978-3-030-72062-9_22

Exploiting generative models for performance predictions of 3D car designs

Published in 2021 IEEE Symposium Series on Computational Intelligence (SSCI), 2021

Recommended citation: Sneha Saha, Thiago Rios, Leandro L. Minku, Niki van Stein, Patricia Wollstadt, Xin Yao, Thomas Bäck, Bernhard Sendhoff, Stefan Menzel, "Exploiting generative models for performance predictions of 3D car designs." 2021 IEEE Symposium Series on Computational Intelligence (SSCI), 2021. https://doi.org/10.1109/ssci50451.2021.9660034

Learning the characteristics of engineering optimization problems with applications in automotive crash

Published in Proceedings of the Genetic and Evolutionary Computation Conference, 2022

Recommended citation: Fu Xing Long, Niki van Stein, Moritz Frenzel, Peter Krause, Markus Gitterle, Thomas Bäck, "Learning the characteristics of engineering optimization problems with applications in automotive crash." Proceedings of the Genetic and Evolutionary Computation Conference, 2022. https://doi.org/10.1145/3512290.3528712

BBOB Instance Analysis: Landscape Properties and Algorithm Performance Across Problem Instances

Published in International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2023

Recommended citation: Fu Xing Long, Diederick Vermetten, Niki van Stein, Anna V. Kononova, "BBOB Instance Analysis: Landscape Properties and Algorithm Performance Across Problem Instances." International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2023. https://doi.org/10.1007/978-3-031-30229-9_25

Adaptive model pruning in federated learning through loss exploration

Published in 2nd Workshop on Advancing Neural Network Training: Computational Efficiency, Scalability, and Resource Optimization (WANT@ ICML 2024), 2024

Recommended citation: Christian Interno, Elena Raponi, Niki van Stein, Thomas Bäck, Markus Olhofer, Yaochu Jin, Barbara Hammer, "Adaptive model pruning in federated learning through loss exploration." 2nd Workshop on Advancing Neural Network Training: Computational Efficiency, Scalability, and Resource Optimization (WANT@ ICML 2024), 2024.

Landscape analysis based vs. domain-specific optimization for engineering design applications: a clear case

Published in 2024 IEEE Conference on Artificial Intelligence (CAI), 2024

Recommended citation: Roy de Winter, Fu Xing Long, Andre Thomaser, Thomas Bäck, Niki van Stein, Anna V. Kononova, "Landscape analysis based vs. domain-specific optimization for engineering design applications: a clear case." 2024 IEEE Conference on Artificial Intelligence (CAI), 2024. https://doi.org/10.1109/cai59869.2024.00148

Landscape-aware automated algorithm configuration using multi-output mixed regression and classification

Published in International Conference on Parallel Problem Solving from Nature, 2024

Recommended citation: Fu Xing Long, Moritz Frenzel, Peter Krause, Markus Gitterle, Thomas Bäck, Niki van Stein, "Landscape-aware automated algorithm configuration using multi-output mixed regression and classification." International Conference on Parallel Problem Solving from Nature, 2024. https://doi.org/10.1007/978-3-031-70068-2_6

Evolutionary computation and explainable AI: A roadmap to understandable intelligent systems

Published in IEEE Transactions on Evolutionary Computation, 2024

Recommended citation: Ryan Zhou, Jaume Bacardit, Alexander Edward Ian Brownlee, Stefano Cagnoni, Martin Fyvie, Giovanni Iacca, John McCall, Niki van Stein, David Walker, Ting Hu, "Evolutionary computation and explainable AI: A roadmap to understandable intelligent systems." IEEE Transactions on Evolutionary Computation, 2024. https://doi.org/10.1109/tevc.2024.3476443

Computational Intelligence: 14th and 15th International Joint Conference on Computational Intelligence (IJCCI 2022 and IJCCI 2023) Revised Selected Papers

Published in Springer Nature, 2025

Recommended citation: Thomas Bäck, Niki van Stein, Christian Wagner, Jonathan M Garibaldi, Francesco Marcelloni, Hak-Keung Lam, Marie Cottrell, Faiyaz Doctor, Joaquim Filipe, Kevin Warwick, Janusz Kacprzyk (Eds.), "Computational Intelligence: 14th and 15th International Joint Conference on Computational Intelligence (IJCCI 2022 and IJCCI 2023) Revised Selected Papers." Springer Nature, 2025.

Controlling the mutation in large language models for the efficient evolution of algorithms

Published in International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2025

Recommended citation: Haoran Yin, Anna V. Kononova, Thomas Bäck, Niki van Stein, "Controlling the mutation in large language models for the efficient evolution of algorithms." International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2025. https://doi.org/10.1007/978-3-031-90065-5_25

BLADE: Benchmark suite for LLM-driven Automated Design and Evolution of iterative optimisation heuristics

Published in Proceedings of the Genetic and Evolutionary Computation Conference Companion, 2025

Recommended citation: Niki van Stein, Anna V. Kononova, Haoran Yin, Thomas Bäck, "BLADE: Benchmark suite for LLM-driven Automated Design and Evolution of iterative optimisation heuristics." Proceedings of the Genetic and Evolutionary Computation Conference Companion, 2025. https://doi.org/10.1145/3712255.3734347

Development of a photonic crystal spectrometer for greenhouse gas measurements

Published in International Conference on Space Optics—ICSO 2024, 2025

Recommended citation: Marijn Siemons, Martijn Veen, Irina Malysheva, Johannes Algera, Stefan Philippi, Kirill Antonov, Niki van Stein, Jérôme Loicq, Nandini Bhattacharya, Rene Berlich, Anna V. Kononova, Ralf Kohlhaas, "Development of a photonic crystal spectrometer for greenhouse gas measurements." International Conference on Space Optics—ICSO 2024, 2025. https://doi.org/10.1117/12.3071597

Gradient Free Multi-Objective Counterfactual Explainability for Multivariate Time Series Classification

Published in 2025 IEEE International Conference on Big Data (BigData), 2025

Recommended citation: Qi Huang, Sofoklis Kitharidis, Furong Ye, Marius Ottolini, Thomas Bäck, Niki van Stein, "Gradient Free Multi-Objective Counterfactual Explainability for Multivariate Time Series Classification." 2025 IEEE International Conference on Big Data (BigData), 2025. https://doi.org/10.1109/bigdata66926.2025.11400892

Benchmarking that Matters: Rethinking Benchmarking in Continuous Optimisation for Practical Impact

Published in International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2026

Recommended citation: Anna V. Kononova, Niki van Stein, Olaf Mersmann, Thomas Bäck, Thomas Bartz-Beielstein, Tobias Glasmachers, Michael Hellwig, Sebastian Krey, Jakub Kůdela, Boris Naujoks, Leonard Papenmeier, Elena Raponi, Quentin Renau, Jeroen Rook, Lennart Schäpermeier, Diederick Vermetten, Daniela Zaharie, "Benchmarking that Matters: Rethinking Benchmarking in Continuous Optimisation for Practical Impact." International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2026. https://doi.org/10.1007/978-3-032-23607-4_20

Investigating the Interplay of Parameterization and Optimizer in Gradient-Free Topology Optimization: A Cantilever Beam Case Study

Published in International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2026

Recommended citation: Jelle Westra, Ivan Olarte Rodriguez, Niki van Stein, Thomas Bäck, Elena Raponi, "Investigating the Interplay of Parameterization and Optimizer in Gradient-Free Topology Optimization: A Cantilever Beam Case Study." International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2026. https://doi.org/10.1007/978-3-032-23607-4_29

LLM Driven Design of Continuous Optimization Problems with Controllable High-Level Properties

Published in International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2026

Recommended citation: Urban Skvorc, Niki van Stein, Moritz Seiler, Britta Grimme, Thomas Bäck, Heike Trautmann, "LLM Driven Design of Continuous Optimization Problems with Controllable High-Level Properties." International Conference on the Applications of Evolutionary Computation (Part of EvoStar), 2026. https://doi.org/10.1007/978-3-032-23607-4_12

Maintenance Planning for Prognostic Health Management of Multi-Component Systems: A Case Study of Multi-Objective Optimisation for Railway Vehicles

Published in PHM Society European Conference, 2026

Recommended citation: Bernd Wagner, Sofoklis Kitharidis, Furong Ye, Thomas Bäck, Niki van Stein, "Maintenance Planning for Prognostic Health Management of Multi-Component Systems: A Case Study of Multi-Objective Optimisation for Railway Vehicles." PHM Society European Conference, 2026. https://doi.org/10.36001/phme.2026.v9i1.5006

Assessing Reproducibility in Evolutionary Computation: A Case Study using Human-and LLM-based Assessment

Published in Proceedings of the Genetic and Evolutionary Computation Conference, 2026

Recommended citation: Francesca Da Ros, Tarik Začiragić, Aske Plaat, Thomas Bäck, Niki van Stein, "Assessing Reproducibility in Evolutionary Computation: A Case Study using Human-and LLM-based Assessment." Proceedings of the Genetic and Evolutionary Computation Conference, 2026. https://arxiv.org/abs/2602.07059

LLaMEA-BO: A Large Language Model Evolutionary Algorithm for Automatically Generating Bayesian Optimization Algorithms

Published in Proceedings of the Genetic and Evolutionary Computation Conference, 2026

Recommended citation: Wenhu Li, Niki van Stein, Thomas Bäck, Elena Raponi, "LLaMEA-BO: A Large Language Model Evolutionary Algorithm for Automatically Generating Bayesian Optimization Algorithms." Proceedings of the Genetic and Evolutionary Computation Conference, 2026. https://doi.org/10.1145/3795095.3805059

Landscape-aware Automated Algorithm Design: An Efficient Framework for Real-world Optimization

Published in Proceedings of the Genetic and Evolutionary Computation Conference, 2026

Recommended citation: Haoran Yin, Shuaiqun Pan, Zhao Wei, Jian Cheng Wong, Yew-Soon Ong, Anna Kononova, Thomas Bäck, Niki van Stein, "Landscape-aware Automated Algorithm Design: An Efficient Framework for Real-world Optimization." Proceedings of the Genetic and Evolutionary Computation Conference, 2026. https://doi.org/10.1145/3795095.3805094

EvoHIIT: Preference-Based Selection in LLM-Assisted Evolutionary Design of Natural Language Solutions

Published in Proceedings of the Genetic and Evolutionary Computation Conference Companion, 2026

Recommended citation: Johana Chen, Niki van Stein, Robert Cabri, Thomas Bäck, Anna V. Kononova, "EvoHIIT: Preference-Based Selection in LLM-Assisted Evolutionary Design of Natural Language Solutions." Proceedings of the Genetic and Evolutionary Computation Conference Companion, 2026. https://doi.org/10.1145/3795101.3814653

Large Language Models for Metaheuristic Design: Exploring Challenges, Limitations, Tools, Benchmarking and Future Opportunities

Published in Proceedings of the Genetic and Evolutionary Computation Conference Companion, 2026

Recommended citation: Roman Senkerik, Niki van Stein, Adam Viktorin, Michal Pluhacek, Thomas Bäck, "Large Language Models for Metaheuristic Design: Exploring Challenges, Limitations, Tools, Benchmarking and Future Opportunities." Proceedings of the Genetic and Evolutionary Computation Conference Companion, 2026. https://doi.org/10.1145/3795101.3807753

Lens-descriptor guided evolutionary algorithm for optimization of complex optical systems with glass choice

Published in International Conference on Parallel Problem Solving from Nature, 2026

Recommended citation: Kirill Antonov, Teus Tukker, Tiago Botari, Thomas Bäck, Anna V. Kononova, Niki van Stein, "Lens-descriptor guided evolutionary algorithm for optimization of complex optical systems with glass choice." International Conference on Parallel Problem Solving from Nature, 2026. https://doi.org/10.1007/978-3-032-36229-2_25

Large language models and evolutionary computation: A critical review of bidirectional interaction, automated algorithm design, and co-adaptive systems

Published in Computer Science Review, 2027

Recommended citation: Dikshit Chauhan, Bapi Dutta, Indu Bala, Niki van Stein, Thomas Bäck, Anupam Yadav, "Large language models and evolutionary computation: A critical review of bidirectional interaction, automated algorithm design, and co-adaptive systems." Computer Science Review, 2027. https://doi.org/10.1016/j.cosrev.2026.101050

talks

Deep Learning, A broad introduction

Published:

Invited talk for the Summer school for Early Stage Researchers. This summer school takes place within the EU project Experience-based Computation: Learning to Optimise (ECOLE), which investigates novel synergies between nature-inspired optimisation and machine learning to address key challenges faced by the European industry.

XAI in Industry

Published:

Invited talk on applications of explainable AI in industry at the SAILS Lunch Time Seminar.

XAI for Healthcare

Published:

Invited talk on explainable AI for healthcare at VZI HealthTech 2024.

Explainable AI

Published:

Invited talk on explainable AI at Alice and Eve 2024.

Evaluating XAI

Published:

Invited talk on evaluating explainable AI at the XAI-NL meetup.

XAI for Time Series

Published:

Invited talk on explainable AI for time series at TU Delft.

Automated Algorithm Design

Published:

Invited talk for the AutoML summer school in Tübingen, Germany (June 10–13, 2025).

Automatic Algorithm Design with LLMs and Evolutionary Computation

Published:

Invited lecture on automatic algorithm design with LLMs and evolutionary computation, covering LLaMEA and how to apply it to real-world cases. Given at the Peking University summer school “Swarm Intelligence & Large Language Models: Intersection, Collision, and Academic Frontiers”.

teaching

Data Science course

Course, Bsc Computer Science, Leiden University, 2022

Data Science places data mining, machine learning and statistics in context, both experimentally and socially. If you want to correctly deploy data mining techniques, you must be able to translate a (broadly formulated) question by a customer or a co-worker into an experimental set-up, to make the right choices for the methods you use, and to be able to process the data in the right form to apply those methods. After performing your experiments, you should not only be able to evaluate the results but also interpret and translate it back to the original question (e.g. by visualization). Socially, data science is of great importance because the media simplify many data-driven results and statistical research, often making mistakes. Thus, a lot of nonsense comes down on us and it is up to you, the data scientists of the future, to recognize, explain and correct that nonsense. This course is a combination of lectures and practical sessions, in which you take a hands-on approach to solving real-world data science problems.

Business Analytics (Minor)

Course, Bsc Computer Science, Leiden University, 2024

Business Analytics places data mining, visualisation, machine learning and statistics in a business context. If you want to correctly deploy data mining / AI techniques, you must be able to translate a (broadly formulated) question by a customer or a co-worker into an experimental set-up, to make the right choices for the methods you use, and to be able to process the data in the right form to apply those methods. After performing your experiments, you should not only be able to evaluate the results but also interpret and translate it back to the original question (e.g. by visualization) and communicate findings to management of colleagues. Socially, data science is of great importance because the media simplify many data-driven results and statistical research, often making mistakes. Thus, a lot of nonsense comes down on us and it is up to you, the data scientists of the future, to recognize, explain and correct that nonsense. This course is a combination of lectures and practical sessions, in which you take a hands-on approach to solving real-world data science problems in a business context.

Applied Data Science and Explainable AI

Course, Bsc Computer Science, Leiden University, 2025

Data Science places data mining, machine learning and statistics in context, both experimentally and socially. If you want to correctly deploy data mining techniques, you must be able to translate a (broadly formulated) question by a customer or a co-worker into an experimental set-up, to make the right choices for the methods you use, and to be able to process the data in the right form to apply those methods. After performing your experiments, you should not only be able to evaluate the results but also interpret and translate it back to the original question (e.g. by visualization). Socially, data science is of great importance because the media simplify many data-driven results and statistical research, often making mistakes. Thus, a lot of nonsense comes down on us and it is up to you, the data scientists of the future, to recognize, explain and correct that nonsense. This course is a combination of lectures and practical sessions, in which you take a hands-on approach to solving real-world data science problems.

Agentic Large Language Models

Master course, Master course, LIACS, Leiden University, 2026

A master course (6 EC) at LIACS on large language models that reason, act and interact. We follow the textbook Agentic Large Language Models (Van Duijn, Van der Meer, Plaat & Van Stein) and teach the course together as the same four authors.