# Convergence and stability of a micro-macro acceleration method:linear slow-fast stochastic differential equations with additive noise

## TL;DR

This paper analyzes the convergence and stability of a micro-macro acceleration method for simulating stiff linear stochastic differential equations with time-scale separation, focusing on additive noise and extrapolation of the slow mean.

## Contribution

It provides a rigorous convergence proof for Gaussian initial distributions and a stability analysis for non-Gaussian laws in the context of the micro-macro acceleration algorithm.

## Key findings

- Proves convergence to microscopic dynamics for Gaussian initial distributions.
- Establishes stability conditions for non-Gaussian initial laws.
- Analyzes the method's behavior on linear SDEs with additive noise.

## Abstract

We analyse the convergence and stability of a micro-macro acceleration algorithm for Monte Carlo simulations of stiff stochastic differential equations with a time-scale separation between the fast evolution of the individual stochastic realizations and some slow macroscopic state variables of the process. The micro-macro acceleration method performs a short simulation of a large ensemble of individual fast paths, before extrapolating the macroscopic state variables of interest over a larger time step. After extrapolation, the method constructs a new probability distribution that is consistent with the extrapolated macroscopic state variables, while minimizing Kullback-Leibler divergence with respect to the distribution available at the end of the Monte Carlo simulation. In the current work, we study the convergence and stability of this method on linear stochastic differential equations with additive noise, when only extrapolating the mean of the slow component. For this case, we prove convergence to the microscopic dynamics when the initial distribution is Gaussian and present a stability result for non-Gaussian initial laws.