2021/07/15 by Kartik G. Waghmare, Waghmare, Kartik G., Victor M. Panaretos +1 · 1 citation
Mathematics · #15A83 #45Q05 (Secondary) #62G05 (Primary) 47A57 #62H22 #62M20 #FOS: Computer and information sciences #FOS: Mathematics #Functional Analysis (math.FA) #Methodology (stat.ME) #Numerical methods in inverse problems #Statistical Methods and Inference #Statistics Theory (math.ST)
paper · pdf · doi:10.48550/arxiv.2107.07350
openalex publication_date 2021/07/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We consider the problem of positive-semidefinite continuation: extending a partially specified covariance kernel from a subdomain Ω of a rectangular domain I× I to a covariance kernel on the entire domain I× I. For a broad class of domains Ω called serrated domains, we are able to present a complete theory. Namely, we demonstrate that a canonical completion always exists and can be explicitly constructed. We characterise all possible completions as suitable perturbations of the canonical completion, and determine necessary and sufficient conditions for a unique completion to exist. We interpret the canonical completion via the graphical model structure it induces on the associated Gaussian process. Furthermore, we show how the estimation of the canonical completion reduces to the solution of a system of linear statistical inverse problems in the space of Hilbert-Schmidt operators, and derive rates of convergence. We conclude by providing extensions of our theory to more general forms of domains, and by demonstrating how our results can be used to construct covariance estimators from sample path fragments of the associated stochastic process. Our results are illustrated numerically by way of a simulation study and a real example.