Stability of Adaptive Gradient Methods
Abstract
Adaptive gradient methods improve convergence by adjusting the step size to local variation. We study a simple update rule and show how stable step sizes reduce oscillation near a stationary point. Experiments compare predictive accuracy, optimization loss, and computational cost.
1. Introduction
Gradient-based optimization is a central component of modern statistical learning. A fixed learning rate is often sensitive to the scale of the objective, motivating methods that adapt the update to the observed gradient. We consider a smooth objective and analyze the resulting trajectory.
Let denote the objective. Starting from an initial parameter vector, the method updates the estimate using a gradient evaluated at the current iterate.
2. Analysis
Our analysis separates the effect of the learning rate from the geometry of the objective. Under a bounded-gradient assumption, the adaptive rule controls the magnitude of each update and yields a stable sequence of iterates. This result motivates the empirical comparison in Table 1.
The step size determines how quickly the method responds to local curvature. A decreasing schedule balances early progress with stable behavior near a stationary point. The same update rule can be applied without changing the underlying objective.