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arXiv 2203.01443cs.LG
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具有前向模式微分的连续时间元学习

Continuous-Time Meta-Learning with Forward Mode Differentiation

Mila(米拉人工智能研究所);Université de Montréal(蒙特利尔大学)

Tristan Deleu, David Kanaa, Leo Feng, Giancarlo Kerg, Yoshua Bengio, Guillaume Lajoie, Pierre-Luc Bacon

摘要:

从具有无限小梯度步长的基于梯度的元学习方法中汲取灵感,我们引入连续时间元学习(COMLN),这是一种元学习算法,其中适应遵循梯度向量场的动态。具体地,输入的表示被元学习,使得任务特定的线性分类器被获得为常微分方程(ODE)的解。将学习过程视为ODE提供了显著的优点,即轨迹的长度现在是连续的,而不是固定和离散数量的梯度步骤。因此,我们可以优化使用随机梯度下降解决新任务所需的适应量,除了学习初始条件外,这是基于梯度的元学习中的标准实践。重要的是,为了计算外循环更新所需的精确元梯度,我们设计了一种基于前向模式微分的高效算法,其内存要求不随学习轨迹的长度而变化,从而允许在恒定内存中进行更长的自适应。我们提供分析保证COMLN的稳定性,我们经验表明其效率在运行时和内存使用方面,我们说明了它的有效性的范围内的Few-Shot图像分类问题。

英文摘要:

Drawing inspiration from gradient-based meta-learning methods with infinitely small gradient steps, we introduce Continuous-Time Meta-Learning (COMLN), a meta-learning algorithm where adaptation follows the dynamics of a gradient vector field. Specifically, representations of the inputs are meta-learned such that a task-specific linear classifier is obtained as a solution of an ordinary differential equation (ODE). Treating the learning process as an ODE offers the notable advantage that the length of the trajectory is now continuous, as opposed to a fixed and discrete number of gradient steps. As a consequence, we can optimize the amount of adaptation necessary to solve a new task using stochastic gradient descent, in addition to learning the initial conditions as is standard practice in gradient-based meta-learning. Importantly, in order to compute the exact meta-gradients required for the outer-loop updates, we devise an efficient algorithm based on forward mode differentiation, whose memory requirements do not scale with the length of the learning trajectory, thus allowing longer adaptation in constant memory. We provide analytical guarantees for the stability of COMLN, we show empirically its efficiency in terms of runtime and memory usage, and we illustrate its effectiveness on a range of few-shot image classification problems.

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