When the Merge Coefficient Stops Mattering: Proximity Regularized Merging for Continual LoRA Adaptation
This study addresses the challenge of LoRA merging in replay-free continual learning, where performance is highly sensitive to merging coefficients and severe interference arises among task vectors. To mitigate these issues, this work proposes a proximity-regularized merging strategy. We theoretically demonstrate that merging performance depends fundamentally on the intrinsic mergeability of task vectors rather than solely on scaling coefficients. Accordingly, a proximity penalty is introduced during training to optimize this property, complemented by a Fisher-weighting mechanism to suppress parameter interference. The proposed approach significantly improves average accuracy across diverse scenarios, effectively broadens the stable range of merging coefficients, and achieves a favorable balance between model stability and plasticity.