Thorsteinn S. Rögnvaldsson

dblp:67/5192 · DBLP profile ↗
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6ranked-venue papers in the field
1as first author
5since 2021 · last 2025
0000-0001-5163-2997ORCID · reported

Domains — venue-derived; a paper can count in several

Data Mining & Knowledge Discovery · 6 (1 first)
YearPublicationVenuePosition
2025 TempEHR: A Temporal Dependency-Based Approach for Synthesizing Electronic Health Records
Emmanuella Budu, Amira Soliman 0002, Farzaneh Etminani, Thorsteinn S. Rögnvaldsson
ECML/PKDD (9)4
2024 Personalized Federated Learning with Contextual Modulation and Meta-Learning
abstract
Federated learning has emerged as a promising approach for training machine learning models on decentralized data sources while preserving data privacy. However, challenges such as communication bottlenecks, heterogeneity of client devices, and non-i.i.d. data distribution pose significant obstacles to achieving optimal model performance. We propose a novel framework that combines federated learning with meta-learning techniques to enhance both efficiency and generalization capabilities. Our approach introduces a federated modulator that learns contextual information from data batches and uses this knowledge to generate modulation parameters. These parameters dynamically adjust the activations of a base model, which operates using a MAML-based approach for model personalization. Experimental results across diverse datasets highlight the improvements in convergence speed and model performance compared to existing federated learning approaches. These findings highlight the potential of incorporating contextual information and meta-learning techniques into federated learning, paving the way for advancements in distributed machine learning paradigms.
Anna Vettoruzzo, Mohamed-Rafik Bouguelia, Thorsteinn S. Rögnvaldsson
SDM3
2023 Towards Explaining Satellite Based Poverty Predictions with Convolutional Neural Networks
abstract
Deep convolutional neural networks (CNNs) have been shown to predict poverty and development indicators from satellite images with surprising accuracy. This paper presents a first attempt at analyzing the CNNs responses in detail and explaining the basis for the predictions. The CNN model, while trained on relatively low resolution day- and night-time satellite images, is able to outperform human subjects who look at high-resolution images in ranking the Wealth Index categories. Multiple explainability experiments performed on the model indicate the importance of the sizes of the objects, pixel colors in the image, and provide a visualization of the importance of different structures in input images. A visualization is also provided of type images that maximize the network prediction of Wealth Index, which provides clues on what the CNN prediction is based on.
Hamid Sarmadi, Thorsteinn S. Rögnvaldsson, Nils Roger Carlsson, Mattias Ohlsson, Ibrahim Wahab, Ola Hall
DSAA2
2023 Practical joint human-machine exploration of industrial time series using the matrix profile
abstract
Abstract Technological advancements and widespread adaptation of new technology in industry have made industrial time series data more available than ever before. With this development grows the need for versatile methods for mining industrial time series data. This paper introduces a practical approach for joint human-machine exploration of industrial time series data using the Matrix Profile, and presents some challenges involved. The approach is demonstrated on three real-life industrial data sets to show how it enables the user to quickly extract semantic information, detect cycles, find deviating patterns, and gain a deeper understanding of the time series. A benchmark test is also presented on ECG (electrocardiogram) data, showing that the approach works well in comparison to previously suggested methods for extracting relevant time series motifs.
Felix Nilsson, Mohamed-Rafik Bouguelia, Thorsteinn S. Rögnvaldsson
Data Min. Knowl. Discov.3
2022 SurvSHAP: A Proxy-Based Algorithm for Explaining Survival Models with SHAP
abstract
Survival Analysis models usually output functions (survival or hazard functions) rather than point predictions like regression and classification models. This makes the explanations of such models a challenging task, especially using the Shapley values. We propose SurvSHAP, a new model-agnostic algorithm to explain survival models that predict survival curves. The algorithm is based on discovering patterns in the predicted survival curves that would identify significantly different survival behaviors, and utilizing a proxy model and SHAP method to explain these distinct survival behaviors. Experiments on synthetic and real datasets demonstrate that the SurvSHAP is able to capture the underlying factors of the survival patterns. Moreover, SurvSHAP results on the Cox Proportional Hazard model are compared with the weights of the model to show that we provide faithful overall explanations, with more fine-grained explanations of the sub-populations. We also illustrate the wrong model and explanations learned by a Cox model when applied to heterogeneous sub-populations. We show that a non-linear machine learning survival model with SurvSHAP can better model the data and provide better explanations than linear models.
Abdallah Alabdallah, Sepideh Pashami, Thorsteinn S. Rögnvaldsson, Mattias Ohlsson
DSAA3
2018 Self-monitoring for maintenance of vehicle fleets
abstract
An approach for intelligent monitoring of mobile cyberphysical systems is described, based on consensus among distributed self-organised agents. Its usefulness is experimentally demonstrated over a long-time case study in an example domain: a fleet of city buses. The proposed solution combines several techniques, allowing for life-long learning under computational and communication constraints. The presented work is a step towards autonomous knowledge discovery in a domain where data volumes are increasing, the complexity of systems is growing, and dedicating human experts to build fault detection and diagnostic models for all possible faults is not economically viable. The embedded, self-organised agents operate on-board the cyberphysical systems, modelling their states and communicating them wirelessly to a back-office application. Those models are subsequently compared against each other to find systems which deviate from the consensus. In this way the group (e.g., a fleet of vehicles) is used to provide a standard, or to describe normal behaviour, together with its expected variability under particular operating conditions. The intention is to detect faults without the need for human experts to anticipate them beforehand. This can be used to build up a knowledge base that accumulates over the life-time of the systems. The approach is demonstrated using data collected during regular operation of a city bus fleet over the period of almost 4 years.
Thorsteinn S. Rögnvaldsson, Slawomir Nowaczyk, Stefan Byttner, Rune Prytz, Magnus Svensson
Data Min. Knowl. Discov.1