arXiv Machine Learning

Reducing the Adaptation Gap Through Reachable Fisher Geometry

arXiv Machine Learning
2d ago

Profile-aware diagnostics of discarded parameter-Hessian mass

The paper evaluates block‑diagonal curvature models by measuring the squared off‑block fraction of the parameter Hessian across different group sizes and curvature profiles. Experiments on CIFAR‑100 ResNet‑18 and a skip‑free variant show that initial discarded fractions are similar but profiles differ, and that shifting from stage to layer groups changes the estimated off‑block mass relative to the profile envelope. Further comparisons on ResNet‑50/Stanford Cars examine off‑group Hessian actions, residuals, and combined candidates, revealing that off‑group input alone often increases minibatch loss, while combined candidates can reduce loss in some cases, with preferences depending on scale and correction‑norm matching.

By Maxim Bolshim (ITMO University, Saint Petersburg, Russia), Alexander Kugaevskikh (ITMO University, Saint Petersburg, Russia)
arXiv Machine Learning
Aug 19

FishBack: Pullback Fisher Geometry for Optimal Activation Steering in Transformers

FishBack introduces a pullback Fisher geometry approach for activation steering in transformers, challenging the common Euclidean assumption of intermediate activation spaces. By deriving a closed‑form steering direction based on the Fisher information metric of the softmax layer, the method achieves target concept changes with minimal off‑target distortion, especially in early and middle layers. Experiments on GPT‑2 Small, Llama‑3‑8B, and Qwen3‑8B demonstrate significant reductions in off‑target KL divergence compared to existing steering baselines.

By Sihan Wang, Jiayi Zhao, Qingyan Cao, Hongbo Yao, Lin Shu
arXiv Machine Learning
Sep 18

FedFIbOS: Fisher Importance based Optimal Submodelling for Heterogeneous Federated Learning

FedFIbOS introduces a Fisher‑importance based criterion for selecting submodel parameters in heterogeneous federated learning, addressing the lack of theoretical justification in prior heuristic methods. By deriving a Fisher‑weighted quadratic masking surrogate and showing that the raw Fisher top‑k rule satisfies this surrogate under a Fisher‑dominant ranking condition, the method preserves convergence guarantees while efficiently estimating Fisher scores from squared gradients. Experiments on CIFAR‑10, CIFAR‑100, and AGNews demonstrate that FedFIbOS outperforms state‑of‑the‑art approaches by roughly 10% in accuracy, especially under strong non‑IID heterogeneity.

By Yasmeen Afzal, Jeremiah D. Deng, Haibo Zhang