Precision matrix estimation
Especially Gaussain
2014-11-16 — 2022-10-03
Wherein the Inversion of the Covariance Is Treated as a Task Beset by Large P and Large N, and Iterative Schemes Such as Conjugate Gradients, Lanczos and QUIC Are Presented as Practical Routes to Approximate Precision Matrices
Estimating the inverse of the covariance matrix means estimating the precision matrices.
Two big data problems can arise here: large \(p\) (ambient dimension) and large \(n\) (sample size). Large \(p\) is a problem because the covariance matrix is a \(p \times p\) matrix and we often need to invert it to calculate some target estimand.
1 The obvious way
Estimate the covariance matrix then invert it. This is the baseline. 🚧TODO🚧
2 QUIC
3 Bayesian
🚧TODO🚧 Wishart priors?
4 Penalised
5 Structured
6 Iterative approximation
Saad (2003)
