Learning from the Descent Direction: Adaptive Gradient Descent under One-Sided H"older Regularity

We study adaptive gradient descent for continuously differentiable, possibly nonconvex objectives under one-sided H"older regularity. Unlike classical H"older- or Lipschitz-gradient assumptions, which control the full gradient variation, our condition bounds only the directional term appearing in the descent inequality. This can allow less conservative step sizes when large gradient changes are orthogonal to, or favorable along, the update direction. We propose an adaptive scalar-step method based on an estimate of positive one-sided H"older curvature, combined with a simple sufficient-decrease safeguard. For nonconvex objectives on a convex region containing the accepted update segments, we prove an explicit best-iterate stationarity bound with a rate determined by the H"older exponent. Unlike predetermined diminishing step-size schemes, the method adapts to the local descent geometry. We evaluate the approach on two full-batch benchmarks designed to separate directional curvature from full gradient variation. On a binary classification problem, the method achieves the lowest final cross-entropy, objective value, and gradient norm, together with the largest classification margin among the compared scalar gradient methods. On a nonconvex H"older regression problem, it attains the lowest final objective gap and gradient norm. These results indicate that one-sided H"older curvature is an effective adaptive step-size signal when full-gradient variation is inflated by directions that do not hinder descent.