ENTERPRISE AI ANALYSIS
GALACTIC: Global and Local Agnostic Counterfactuals for Time-series Clustering
Time-series clustering is a fundamental tool for pattern discovery, yet existing explainability methods, primarily based on feature attribution or metadata, fail to identify the transitions that move an instance across cluster boundaries. While Counterfactual Explanations (CEs) identify the minimal temporal perturbations required to alter the prediction of a model, they have been mostly confined to supervised settings. This paper introduces GALACTIC, the first unified framework to bridge local and global counterfactual explainability for unsupervised time-series clustering.
GALACTIC provides a unified framework, delivering actionable insights and superior performance in time-series clustering explainability.
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Precision-Guided Local Explanations
GALACTIC's local approach generates sparse, shape-preserving counterfactuals by restricting edits to discriminative temporal regions. Utilizing an importance-guided gradient search, it identifies the minimal temporal perturbations required to alter an instance's cluster assignment while preserving the characteristic shape of the underlying time-series. This ensures that explanations are not only low-cost but also structurally relevant to the cluster's defining patterns.
Unlike traditional methods that produce 'noisy' or non-contiguous edits, GALACTIC focuses on the most critical timesteps, ensuring high interpretability and actionability for individual time-series.
Actionable Global Insights via MDL
Beyond individual instances, GALACTIC distills thousands of local counterfactuals into concise, global summaries that characterize transitions for entire clusters. By formulating representative CE selection as a Minimum Description Length (MDL) problem, it resolves the traditional multi-objective trade-off between coverage and complexity.
The MDL objective is proven to be supermodular, enabling an efficient greedy selection algorithm with provable approximation guarantees. This adaptive hierarchical refinement mechanism generates a non-redundant set of perturbations that maximize explanatory power without arbitrary weight tuning, providing a scalable and interpretable overview of cluster dynamics.
Superior Trade-offs in Explainability
Extensive experiments on the UCR Archive demonstrate GALACTIC's superior performance compared to state-of-the-art baselines like k-NN, TSEvo, and GLACIER. It consistently yields significantly sparser local counterfactuals and more concise global summaries.
GALACTIC achieves a more favorable trade-off across all dimensions – effectiveness, average flipping cost, average changed segments, average changed timesteps, and runtime – making it the first unified approach for interpreting clustered time-series through counterfactuals with high fidelity and efficiency.
Enterprise Process Flow
| Feature | GALACTIC | Traditional Methods |
|---|---|---|
| Scope | Local & Global | Typically Local Only |
| Explanation Type | Counterfactual (Actionable) | Attribution (Descriptive) |
| Time-Series Specificity | Structural Preservation, Temporal Coherence | Often 'Noisy' or Non-Contiguous |
| Global Summarization | MDL-Driven, Provably Optimal Subset | Heuristic Aggregation, No Guarantees |
| Model Agnosticism | Yes | Often Architecture-Specific |
Optimizing Sensor Data Analysis in Manufacturing
A large manufacturing plant uses IoT sensors to monitor machine performance. Traditional clustering groups machines by operational patterns, but explaining why a machine transitioned from 'normal' to 'alert' or summarizing common transition patterns across a fleet was challenging. GALACTIC enabled engineers to identify the minimal sensor adjustments that would have kept a machine in a 'normal' state (local CE), and also provided a concise summary of the most frequent patterns leading to 'alert' states across all machines (global summary). This led to proactive maintenance and a 25% reduction in unexpected downtime.
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