Accelerated Zeroth-Order and First-Order Momentum Methods from Mini to Minimax Optimization
Feihu HuangShangqian GaoJian PeiHeng Huang
Develops momentum-based accelerated zeroth-order and first-order algorithms for nonconvex minimization and minimax problems that achieve state-of-the-art query and gradient complexities without relying on large batch sizes.
Modern machine learning applications increasingly rely on complex optimization, ranging from training models against adversarial attacks to solving multi-agent decision problems. However, calculating exact mathematical gradients is often impractical or impossible, especially in black-box systems where practitioners can only observe model outputs rather than internal calculations. While gradient-free and minimax optimization techniques exist, standard approaches suffer from high computational noise and typically require impractically large data batches at every iteration, leading to excessive evaluation costs and slow processing.
The article aims to resolve these computational bottlenecks by introducing a family of accelerated momentum-based algorithms for both single-objective minimization and two-player minimax optimization. Specifically, the authors evaluate whether combining momentum-based noise reduction with uniform smoothing techniques can achieve provably faster convergence and lower query costs in both gradient-free and gradient-accessible settings, with and without variable constraints.
To demonstrate this, the authors develop theoretical proofs establishing query and gradient complexity bounds for both constrained and unconstrained problems. They also validate their theoretical guarantees through practical computational experiments, including generating black-box adversarial attacks against deep neural networks across standard image benchmarks (MNIST, FashionMNIST, CIFAR-10, and SVHN) and simulating data poisoning attacks on logistic regression models.
The findings show that the proposed gradient-free minimization method reduces function query complexity while operating efficiently with a single data sample per step, eliminating the need for large batch updates required by existing baseline methods. For black-box minimax problems, the accelerated method matches or improves upon existing convergence rates without large batches. For transparent minimax problems where gradients can be calculated directly, the proposed first-order algorithm achieves state-of-the-art computational efficiency. In empirical testing, these algorithms consistently required substantially fewer function evaluations to successfully compromise target models compared to previous techniques.
These results demonstrate that organizations conducting security audits, adversarial robustness testing, and complex optimization can significantly cut computing time and infrastructure expenses. Removing the requirement for massive batch sizes enables real-world deployment in resource-constrained environments where querying a black-box model is computationally expensive or rate-limited.
Technical leaders and engineering teams should consider adopting these momentum-based variance-reduction methods when auditing machine learning models for adversarial vulnerabilities or solving saddle-point games. Practitioners should evaluate these techniques in pilot benchmarking workflows to optimize hyperparameter selection across their specific domain tasks before wide-scale deployment.
Readers should note that the theoretical guarantees rely on component smoothness and strong concavity in the minimax sub-problems, which may not hold uniformly across every non-standard architecture. Nevertheless, given the consistent performance across both mathematical proofs and empirical benchmarks, confidence in the algorithms' computational advantages remains high.
- Paper: Stochastic First- and Zeroth-Order Methods for Nonconvex Stochastic Programming, Saeed Ghadimi et al. (2013). Establishes foundational convergence analysis and randomized smoothing frameworks for stochastic first-order and zeroth-order nonconvex optimization.
- Paper: ZOO: Zeroth Order Optimization Based Black-box Attacks to Deep Neural Networks without Training Substitute Models, Pin-Yu Chen et al. (2017). Introduces the formulation and practical application of zeroth-order optimization for black-box adversarial attacks on deep neural networks.
- Paper: Towards Deep Learning Models Resistant to Adversarial Attacks, Aleksander Madry et al. (2017). Frames adversarial machine learning as a robust minimax optimization problem, motivating the descent-ascent algorithms studied in the source.
- Paper: Fine-Tuning Language Models with Just Forward Passes, Sadhika Malladi et al. (2023). Applies memory-efficient zeroth-order optimization principles to large-scale deep learning by fine-tuning massive language models purely via forward passes.
- Paper: Lower Bounds and Accelerated Algorithms for Bilevel Optimization, Kaiyi Ji et al. (2023). Extends accelerated first-order optimization principles and lower-bound complexity analysis from minimax problems to structured bilevel optimization.
