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A nonzero-mean Gaussian process with correlated observation noise
Example
Let , let , , , and let for all . Observe at with noise covariance and evaluate the selected Gaussian conditional-kernel version at for the test index . The posterior law is .
Facts & Assumptions
Given: AC; the finite index set and mean above; the constant covariance kernel; and observation noise with law .
AC is required by the finite Gaussian-process and multivariate-normal constructions. The Axiom of Choice
Any symmetric positive-semidefinite kernel on an arbitrary set defines a canonical cylinder-space Gaussian process under AC. A mean and positive-semidefinite kernel define a Gaussian process
Under AC, every finite symmetric positive-semidefinite covariance matrix defines a possibly singular Gaussian law. Multivariate normal law, including singular covariance
A finite product of sigma-finite measures exists and has the rectangle product formula. For sigma-finite factors, the product measure exists, has the rectangle formula, is sigma-finite, and is unique
Product-coordinate random elements are independent when their rectangle probabilities factor. Independent random elements Independent random elements are characterized by finite rectangle probabilities
Coordinates on the cylinder sigma-algebra are measurable, and a finite product sigma-algebra is generated by its coordinate sets. Coordinate maps, finite-coordinate cylinders, and the cylinder -algebra The product sigma-algebra and its finite iterates
With positive-definite observed covariance , the Gaussian conditional kernel has mean and covariance . Finite Gaussian-process posterior and predictive laws
Verification
Given: The parameters and observed value in the Example.
For every finite coefficient list on , the constant kernel has quadratic form . The noise matrix is positive definite because for . By [F1] there is a cylinder-space GP law and [F2] gives the noise law. Their product probability exists by [F3]; its process and noise coordinates are measurable by [F5] and independent by [F4]. Thus this is a model satisfying the theorem's noise assumption.
The observed and test covariance blocks are , , and . Thus , which is positive definite since its quadratic form is . Direct multiplication gives .
Since , , and , and . The posterior mean in [F6] is therefore .
Also , so . The posterior variance is , proving the displayed conditional-kernel value. This is the value of the all- kernel version specified in [F6] at ; the theorem does not make conditional-law values pointwise unique.
Depends on
- The Axiom of Choice
- Coordinate maps, finite-coordinate cylinders, and the cylinder $\sigma$-algebra
- Independent random elements
- Multivariate normal law, including singular covariance
- The product sigma-algebra and its finite iterates
- Finite Gaussian-process posterior and predictive laws
- A mean and positive-semidefinite kernel define a Gaussian process
- Independent random elements are characterized by finite rectangle probabilities
- For sigma-finite factors, the product measure exists, has the rectangle formula, is sigma-finite, and is unique
Used by
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Sources
- A. W. van der Vaart and J. H. van Zanten, Reproducing kernel Hilbert spaces of Gaussian priors (2008) (standard reference, not scraped)
- Carl Edward Rasmussen and Christopher K. I. Williams, Gaussian Processes for Machine Learning (MIT Press, 2006), Chapter 2 (standard reference, not scraped)