论文标题
部分可观测时空混沌系统的无模型预测
Understanding Deep Learning using Topological Dynamical Systems, Index Theory, and Homology
论文作者
论文摘要
储层计算是预测湍流的有力工具,其简单的架构具有处理大型系统的计算效率。然而,其实现通常需要完整的状态向量测量和系统非线性知识。我们使用非线性投影函数将系统测量扩展到高维空间,然后将其输入到储层中以获得预测。我们展示了这种储层计算网络在时空混沌系统上的应用,该系统模拟了湍流的若干特征。我们表明,使用径向基函数作为非线性投影器,即使只有部分观测并且不知道控制方程,也能稳健地捕捉复杂的系统非线性。最后,我们表明,当测量稀疏、不完整且带有噪声,甚至控制方程变得不准确时,我们的网络仍然可以产生相当准确的预测,从而为实际湍流系统的无模型预测铺平了道路。
In this paper we investigate Deep Learning Models using topological dynamical systems, index theory, and computational homology. These mathematical machinery was invented initially by Henri Poincare around 1900 and developed over time to understand shapes and dynamical systems whose structure and behavior is too complicated to solve for analytically but can be understood via global relationships. In particular, we show how individual neurons in a neural network can correspond to simplexes in a simplicial complex manifold approximation to the decision surface learned by the NN, and how these simplexes can be used to compute topological invariants from algebraic topology for the decision manifold with an explicit computation of homology groups by hand in a simple case. We also show how the gradient of the probability density function learned by the NN creates a dynamical system, which can be analyzed by a myriad of topological tools such as Conley Index Theory, Morse Theory, and Stable Manifolds. We solve analytically for associated the differential equation for a trained NN with a single hidden layer of 256 Neurons applied to the MINST digit dataset, and approximately numerically that it a sink and basin of attraction for each of the 10 classes, but the sinks and strong attracting manifolds lie in regions not corresponding to images of actual digits. Index theory implies the existence of saddles. Level sets of the probability functions are 783-dimensional manifolds which can only change topology at critical points of the dynamical system, and these changes in topology can be investigated with Morse Theory.