Full contraction analysis of the composed slice map

Derive a full contraction analysis for the composed CORAM slice map, including the effects of correlated or uneven expert updates and the manifold means over the rotation, spectral-shift, and Stiefel factors.

Background

CORAM uses an amplification factor to compensate for the contraction produced by averaging expert-specific factors on curved spaces. Proposition 1 establishes a N\sqrt{N} amplification scale only under idealized assumptions of pairwise orthogonal updates with equal norms, while the empirically measured cRMSc_{\mathrm{RMS}} is intended to account for correlated or uneven updates.

The paper reports empirical values for the restoration strength κ\kappa, including a high-dispersion value calibrated on only one base model. A general theoretical characterization of the contraction induced by the complete composed slice transformation remains unresolved.

References

A full contraction analysis of the composed slice map remains open.

CORAM: Coherent Orthogonal Rotation for Model Merging  (2608.17366 - Sui et al., 18 Aug 2026) in Section ‘Limitations,’ paragraph ‘Scale and strength’