arXiv subjects

Nada Cvetković

Publications and source records attributed to Nada Cvetković.

4 recordsLinked to original sources

arXiv2025

Upper and lower bounds for local Lipschitz stability of Bayesian posteriors

The work of Sprungk (Inverse Problems, 2020) established the local Lipschitz continuity of the misfit-to-posterior and prior-to-posterior maps with respect to the Kullback--Leibler divergence and the total variation, Hellinger, and 1-Wasserstein metrics, by proving certain upper bounds. The upper bounds were also used to show that if a posterior measure is more concentrated, then it can be more sensitive to perturbations in the misfit or prior. We prove upper bounds and lower bounds that emphasise the importance of the evidence. The lower bounds show that the sensitivity of posteriors to perturbations in the misfit or the prior not only can increase, but in general will increase as the posterior measure becomes more concentrated, i.e. as the evidence decreases to zero. Using the explicit dependence of our bounds on the evidence, we identify sufficient conditions for the misfit-to-posterior and prior-to-posterior maps to be locally bi-Lipschitz continuous.

math.ST↗

arXiv2024

Choosing observation operators to mitigate model error in Bayesian inverse problems

In statistical inference, a discrepancy between the parameter-to-observable map that generates the data and the parameter-to-observable map that is used for inference can lead to misspecified likelihoods and thus to incorrect estimates. In many inverse problems, the parameter-to-observable map is the composition of a linear state-to-observable map called an `observation operator' and a possibly nonlinear parameter-to-state map called the `model'. We consider such Bayesian inverse problems where the discrepancy in the parameter-to-observable map is due to the use of an approximate model that differs from the best model, i.e. to nonzero `model error'. Multiple approaches have been proposed to address such discrepancies, each leading to a specific posterior. We show how to use local Lipschitz stability estimates of posteriors with respect to likelihood perturbations to bound the Kullback--Leibler divergence of the posterior of each approach with respect to the posterior associated to the best model. Our bounds lead to criteria for choosing observation operators that mitigate the effect of model error for Bayesian inverse problems of this type. We illustrate one such criterion on an advection-diffusion-reaction PDE inverse problem from the literature, and use this example to discuss the importance and challenges of model error-aware inference.

math.ST↗

arXiv2020

A convergent discretisation method for transition path theory for diffusion processes

Transition path theory (TPT) for diffusion processes is a framework for analysing the transitions of multiscale ergodic diffusion processes between disjoint metastable subsets of state space. Most methods for applying TPT involve the construction of a Markov state model on a discretisation of state space that approximates the underlying diffusion process. However, the assumption of Markovianity is difficult to verify in practice, and there are to date no known error bounds or convergence results for these methods. We propose a Monte Carlo method for approximating the forward committor, probability current, and streamlines from TPT for diffusion processes. Our method uses only sample trajectory data and partitions of state space based on Voronoi tessellations. It does not require the construction of a Markovian approximating process. We rigorously prove error bounds for the approximate TPT objects and use these bounds to show convergence to their exact counterparts in the limit of arbitrarily fine discretisation. We illustrate some features of our method by application to a process that solves the Smoluchowski equation on a triple-well potential.

math.NA↗

arXiv2019

On a degeneracy ratio for bounded convex polytopes

We consider a quantity that measures the roundness of a bounded, convex $d$-polytope in $\mathbb{R}^d$. We majorise this quantity in terms of the smallest singular value of the matrix of outer unit normals to the facets of the polytope.

math.OC↗