81 research outputs found
A new framework for extracting coarse-grained models from time series with multiscale structure
In many applications it is desirable to infer coarse-grained models from
observational data. The observed process often corresponds only to a few
selected degrees of freedom of a high-dimensional dynamical system with
multiple time scales. In this work we consider the inference problem of
identifying an appropriate coarse-grained model from a single time series of a
multiscale system. It is known that estimators such as the maximum likelihood
estimator or the quadratic variation of the path estimator can be strongly
biased in this setting. Here we present a novel parametric inference
methodology for problems with linear parameter dependency that does not suffer
from this drawback. Furthermore, we demonstrate through a wide spectrum of
examples that our methodology can be used to derive appropriate coarse-grained
models from time series of partial observations of a multiscale system in an
effective and systematic fashion
Stochastic Differential Equations with Variational Wishart Diffusions
We present a Bayesian non-parametric way of inferring stochastic differential
equations for both regression tasks and continuous-time dynamical modelling.
The work has high emphasis on the stochastic part of the differential equation,
also known as the diffusion, and modelling it by means of Wishart processes.
Further, we present a semi-parametric approach that allows the framework to
scale to high dimensions. This successfully lead us onto how to model both
latent and auto-regressive temporal systems with conditional heteroskedastic
noise. We provide experimental evidence that modelling diffusion often improves
performance and that this randomness in the differential equation can be
essential to avoid overfitting.Comment: ICML 202
Semi-Parametric Drift and Diffusion Estimation for Multiscale Diffusions
We consider the problem of statistical inference for the effective dynamics
of multiscale diffusion processes with (at least) two widely separated
characteristic time scales. More precisely, we seek to determine parameters in
the effective equation describing the dynamics on the longer diffusive time
scale, i.e. in a homogenization framework. We examine the case where both the
drift and the diffusion coefficients in the effective dynamics are
space-dependent and depend on multiple unknown parameters. It is known that
classical estimators, such as Maximum Likelihood and Quadratic Variation of the
Path Estimators, fail to obtain reasonable estimates for parameters in the
effective dynamics when based on observations of the underlying multiscale
diffusion. We propose a novel algorithm for estimating both the drift and
diffusion coefficients in the effective dynamics based on a semi-parametric
framework. We demonstrate by means of extensive numerical simulations of a
number of selected examples that the algorithm performs well when applied to
data from a multiscale diffusion. These examples also illustrate that the
algorithm can be used effectively to obtain accurate and unbiased estimates.Comment: 32 pages, 10 figure
Weak symmetries of stochastic differential equations driven by semimartingales with jumps
Stochastic symmetries and related invariance properties of \ufb01nite dimensional SDEs driven by
general c`adl`ag semimartingales taking values in Lie groups are de\ufb01ned and investigated. The
considered set of SDEs, \ufb01rst introduced by S. Cohen, includes a\ufb03ne and Marcus type SDEs as
well as smooth SDEs driven by L\ub4evy processes and iterated random maps. A natural extension to
this general setting of reduction and reconstruction theory for symmetric SDEs is provided. Our
theorems imply as special cases non trivial invariance results concerning a class of a\ufb03ne iterated
random maps as well as (weak) symmetries for numerical schemes (of Euler and Milstein type) for
Brownian motion driven SDEs
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