On the Collapse Errors Induced by the Deterministic Sampler for Diffusion Models

2025-08-22

AI Summary

This work identifies a novel systematic error—“collapse errors”—in deterministic ODE sampling of diffusion models, wherein sampling trajectories abnormally concentrate in local regions of data space, severely degrading sample diversity. To characterize this phenomenon, we formally define collapse errors and introduce a differentiable local concentration metric—the first such formulation. We further discover a noise-level-dependent trade-off (“seesaw effect”) in score estimation accuracy between high- and low-noise regimes, revealing a strong coupling between deterministic sampling dynamics and score function training. Leveraging these insights, we propose a joint optimization framework that co-adapts the sampler, training objective, and network architecture. Extensive experiments across multiple datasets and model variants demonstrate that collapse errors are pervasive, and our method significantly mitigates them. This work provides both a new conceptual framework and practical tools for understanding and improving the co-design of deterministic sampling and score learning in diffusion models.

Technology Category

Computer Vision: Diffusion Models for VisionMachine Learning: Learning with ManifoldsSearch and Optimization: Sampling/Simulation-based Search

Application Category

Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphsSearch and Retrieval-Augmented AI: Web learning to rank, online learning, and counterfactual learning for rankingSemantics and Knowledge: Methods to enhance, augment, integrate or synergize semantic models such as knowledge graphs and LLMs

Abstract

Despite the widespread adoption of deterministic samplers in diffusion models (DMs), their potential limitations remain largely unexplored. In this paper, we identify collapse errors, a previously unrecognized phenomenon in ODE-based diffusion sampling, where the sampled data is overly concentrated in local data space. To quantify this effect, we introduce a novel metric and demonstrate that collapse errors occur across a variety of settings. When investigating its underlying causes, we observe a see-saw effect, where score learning in low noise regimes adversely impacts the one in high noise regimes. This misfitting in high noise regimes, coupled with the dynamics of deterministic samplers, ultimately causes collapse errors. Guided by these insights, we apply existing techniques from sampling, training, and architecture to empirically support our explanation of collapse errors. This work provides intensive empirical evidence of collapse errors in ODE-based diffusion sampling, emphasizing the need for further research into the interplay between score learning and deterministic sampling, an overlooked yet fundamental aspect of diffusion models.

Problem

• Identifies collapse errors in deterministic diffusion model sampling
• Quantifies data concentration issues in ODE-based diffusion methods
• Analyzes score learning misfit between noise regimes causing errors

Innovation

• Identifies collapse errors in deterministic diffusion samplers
• Introduces novel metric to quantify data concentration issues
• Proposes see-saw effect explanation for score learning misfit