Efficient Statistically Accurate Algorithms for the Fokker-Planck Equation in Large Dimensions

TL;DR

This paper introduces efficient algorithms for solving high-dimensional Fokker-Planck equations that accurately capture complex, intermittent probability distributions in turbulent systems using a hybrid Gaussian mixture approach.

Contribution

The paper develops a hybrid parametric-nonparametric algorithm that overcomes the curse of dimensionality and accurately models non-Gaussian PDFs in high-dimensional turbulent systems.

Findings

Efficient algorithms require only a small number of ensembles.

The method accurately captures fat-tailed, intermittent PDFs.

It outperforms traditional particle methods in high dimensions.

Abstract

Solving the Fokker-Planck equation for high-dimensional complex turbulent dynamical systems is an important and practical issue. However, most traditional methods suffer from the curse of dimensionality and have difficulties in capturing the fat tailed highly intermittent probability density functions (PDFs) of complex systems in turbulence, neuroscience and excitable media. In this article, efficient statistically accurate algorithms are developed for solving both the transient and the equilibrium solutions of Fokker-Planck equations associated with high-dimensional nonlinear turbulent dynamical systems with conditional Gaussian structures. The algorithms involve a hybrid strategy that requires only a small number of ensembles. Here, a conditional Gaussian mixture in a high-dimensional subspace via an extremely efficient parametric method is combined with a judicious non-parametric Gaussian kernel density estimation in the remaining low-dimensional subspace. Particularly, the parametric method provides closed analytical formulae for determining the conditional Gaussian distributions in the high-dimensional subspace and is therefore computationally efficient and accurate. The full non-Gaussian PDF of the system is then given by a Gaussian mixture. Different from the traditional particle methods, each conditional Gaussian distribution here covers a significant portion of the high-dimensional PDF. Therefore a small number of ensembles is sufficient to recover the full PDF, which overcomes the curse of dimensionality. Notably, the mixture distribution has a significant skill in capturing the transient behavior with fat tails of the high-dimensional non-Gaussian PDFs, and this facilitates the algorithms in accurately describing the intermittency and extreme events in complex turbulent systems.