A New First-Order Meta-Learning Algorithm with Convergence Guarantees

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arXiv:2409.03682v2 Announce Type: replace Abstract: Learning new tasks by leveraging prior experience is a fundamental trait of intelligent systems. While Model-Agnostic Meta-Learning (MAML) is a leading approach, it suffers from significant computational and memory overhead due to the requirement of computing second-order meta-gradients. We propose \textbf{FO-B-MAML}, a novel first-order variant of MAML derived from a bi-level optimization perspective. Our framework introduces a new expression of the meta-gradient, defined as the derivative of the solution of a perturbed optimization problem. This formulation allows the meta-gradient to be estimated using various finite difference methods; in this work, we propose and analyze two simple yet effective estimators: a forward and a symmetric approximation. Unlike existing first-order methods like FO-MAML and Reptile, which suffer from irreducible bias, we prove that FO-B-MAML converges to a stationary point of the meta-objective. Notably, the symmetric estimator achieves an improved $\mathcal{O}(\delta^{2/3})$ bias rate, strictly enhancing previous first-order theory. Furthermore, we demonstrate that the MAML objective violates standard smoothness assumptions; we show instead that its smoothness constant grows with the norm of the meta-gradient. This property theoretically justifies the use of normalized or clipped-gradient methods (SNGDM) over vanilla gradient descent. Our empirical results validate these advancements: FO-B-MAML achieves high accuracy, closely following second-order MAML performance. Crucially, our method …

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