Recover the competitor direction of a collapsed class

Develop an off-diagonal posterior treatment for the final classification layer that determines which competing aircraft class a collapsed class is losing to, thereby extending the diagonal Laplace bias-variance measure from an undirected collapse indicator to a directed class-pair diagnosis.

Background

The collapsed quantity is the posterior variance of a class-specific bias parameter under a diagonal Laplace approximation. It can identify that a class is collapsing because of data scarcity, but it cannot determine the competitor toward which the class collapses.

The missing direction is a cross-class relation requiring off-diagonal covariance in the last-layer posterior. The paper explicitly leaves development of such a directed treatment unresolved because the richer posterior would be more expensive and harder to stabilize.

References

Recovering it would need a more expensive, harder-to-stabilize off-diagonal posterior. We regard the undirected form as the instrument's honest scope and leave a directed treatment to future work.

— Not All Confusion Is Equal: A Source-Aware Uncertainty Diagnosis for Fine-Grained Aircraft Detection  (2609.29959 - Huang et al., 24 Sep 2026) in Section 5.2, subsection “The collapsed quantity has no direction”