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This paper introduces Semantic Space Search Trajectory Networks (STNs), a novel graph-based framework for visualizing optimization algorithm behavior in semantic spaces, which allows for the analysis of learning dynamics across diverse algorithm families. By discretizing semantic vectors and employing agglomerative clustering, the authors demonstrate that STNs can effectively characterize differences in model performance in both classification and regression tasks. The findings reveal that training on real labels results in denser and more centralized STNs compared to training on shuffled labels, highlighting the impact of data quality on learning dynamics.
Semantic Space STNs reveal that training on real labels leads to more efficient learning dynamics, contrasting sharply with the effects of label randomization.
Search Trajectory Networks (STNs) are a graph-based tool for visualizing and characterizing the behavior of optimization algorithms. STNs'reliance on discretization of the search space has largely confined them to low-dimensional or combinatorial settings. We introduce a methodology for constructing STNs in semantic spaces, defined as the space of a model's predictions on a fixed sample set. Our approach discretizes semantic vectors and aggregates them into network nodes via agglomerative clustering with complete linkage under a normalized Hamming distance. Since any predictor can be summarized by its semantic vector, this method enables comparison of learning dynamics across otherwise incomparable algorithm families. We apply semantic space STNs to classification and regression tasks solved using different machine learning algorithms, recovering known qualitative differences between them. Additionally, we use semantic space STNs to study neural network generalization by contrasting standard training with the label randomization regime of Zhang et al. (2017). The resulting STNs exhibit consistent structural differences, training on real labels produces denser, more efficient and more centralized graphs than training on shuffled labels. Together, our results show that semantic space STNs capture functional training dynamics arising from the interaction between learning algorithms and data, providing a tool for analyzing and comparing learning dynamics across machine learning models and training regimes.