Mathematical methods are developed to characterize the asymptotics of recurrent neural networks (RNN) as the number of hidden units, data samples in the sequence, hidden state updates, and training steps simultaneously grow to infinity. In the case of an RNN with a simplified weight matrix, we prove the convergence of the RNN to the solution of an infinite-dimensional ODE coupled with the fixed point of a random algebraic equation. The analysis requires addressing several challenges which are unique to RNNs. In typical mean-field applications (e.g., feedforward neural networks), discrete updates are of magnitude $\mathcal{O}(\frac{1}{N})$ and the number of updates is $\mathcal{O}(N)$. Therefore, the system can be represented as an Euler approximation of an appropriate ODE/PDE, which it will converge to as $N \rightarrow \infty$. However, the RNN hidden layer updates are $\mathcal{O}(1)$. Therefore, RNNs cannot be represented as a discretization of an ODE/PDE and standard mean-field techniques cannot be applied. Instead, we develop a fixed point analysis for the evolution of the RNN memory states, with convergence estimates in terms of the number of update steps and the number of hidden units. The RNN hidden layer is studied as a function in a Sobolev space, whose evolution is governed by the data sequence (a Markov chain), the parameter updates, and its dependence on the RNN hidden layer at the previous time step. Due to the strong correlation between updates, a Poisson equation must be used to bound the fluctuations of the RNN around its limit equation. These mathematical methods give rise to the neural tangent kernel (NTK) limits for RNNs trained on data sequences as the number of data samples and size of the neural network grow to infinity.

开发数学方法来表征随着隐藏单元数量、数据样本序列、隐藏状态更新和训练步骤同时趋向于无穷大，递归神经网络（RNN）的渐近特性。通过研究联合随机代数方程的无穷维ODE的解，我们证明了简化权重矩阵的RNN收敛到一个无穷维ODE的解与固定点耦合。这项分析需要解决针对RNN独特的几个挑战，而标准的均场技术无法应用于RNN，因此我们开发了一种用于RNN记忆状态演进的固定点分析方法，并对更新步骤和隐藏单元数量给出了收敛估计。当数据样本和神经网络规模趋向于无穷大时，这些数学方法导致了RNN在数据序列上训练时的神经切向核（NTK）极限。

递归神经网络在符合遍历性数据序列上训练的核极限