Ergodic and Foliated Kernel-Differentiation Method for Linear Responses of Random Systems
摘要
We extend the kernel-differentiation method for the linear response (parameter derivative of averaged observables) of random dynamical systems. First, for the linear response of physical (or stationary) measures, we extend the method to an ergodic version, which is sampled by an infinitely long sample path, so it is more efficient than previous results. This is achieved by combining the likelihood ratio trick, decay of correlations, and ergodic theorem. Second, when the noise and perturbation are along a given foliation, we show that the method is still valid for both finite and infinite time. These results are derived using basic calculus via a microscopic view of transfer operators.
We use the ergodic formula to numerically compute the linear response of a tent map with additive noise. We use the foliated formula to compute the linear response of an unstable neural network with 51 layers
Finally, we derive the three basic linear response methods (path perturbation, divergence, and kernel-differentiation methods) in simplified settings and propose a potential future program unifying them.