arXiv:2505.13578cs.LG2025-05

不依赖梯度的测试时优化方法,打破对称性以降低不变成本函数值。

Symmetry-Breaking Descent for Invariant Cost Functionals

  • 通过构造流形上的变分流,利用李代数生成对称性破缺变形
  • 在弱耦合条件下,可使不变成本函数值显著降低
  • 适用于无标签、不可导的机器学习评估指标优化

我们研究在全局对称群 $G \subset \mathrm{Diff}(M)$ 作用下,对定义在 Sobolev 空间 $H^s(M)$ 上的信号 $S$ 的任务成本泛函 $W : H^s(M) \to \mathbb{R}$ 的最小化问题,该泛函不假设连续或可微。群 $G$ 通过拉回作用于信号,而 $W$ 在此作用下保持不变。此类情形常见于机器学习和相关优化任务中,性能度量可能不连续或依赖模型内部结构。我们提出一种变分方法,利用对称性结构构造输入信号的显式变形。通过最小化辅助能量泛函获得变形控制场 $\phi: M \to \mathbb{R}^d$,其诱导的流通常位于 $S$ 的 $G$-轨道的法空间(相对于 $L^2$ 内积),因此是跨越 $G$-不变成本决策边界的自然候选。我们分析了两种耦合项形式:(1) 纯几何,与 $W$ 无关;(2) 与 $W$ 弱耦合。在温和条件下,证明了对称性破缺变形能降低成本。该方法无需梯度反向传播或训练标签,完全在测试时运行,为通过李代数变分流优化不连续不变成本泛函提供了原则性工具。

原文摘要 · Abstract (English)

We study the problem of reducing a task cost functional $W : H^s(M) \to \mathbb{R}$, not assumed continuous or differentiable, defined over Sobolev-class signals $S \in H^s(M) $, in the presence of a global symmetry group $G \subset \mathrm{Diff}(M)$. The group acts on signals by pullback, and the cost $W$ is invariant under this action. Such scenarios arise in machine learning and related optimization tasks, where performance metrics may be discontinuous or model-internal. We propose a variational method that exploits the symmetry structure to construct explicit deformations of the input signal. A deformation control field $ ϕ: M \to \mathbb R^d$, obtained by minimizing an auxiliary energy functional, induces a flow that generically lies in the normal space (with respect to the $L^2$ inner product) to the $G$-orbit of $S$, and hence is a natural candidate to cross the decision boundary of the $G $-invariant cost. We analyze two variants of the coupling term: (1) purely geometric, independent of $W$, and (2) weakly coupled to $W$. Under mild conditions, we show that symmetry-breaking deformations of the signal can reduce the cost. Our approach requires no gradient backpropagation or training labels and operates entirely at test time. It provides a principled tool for optimizing discontinuous invariant cost functionals via Lie-algebraic variational flows.

变分优化对称性破缺测试时优化不变性

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