## The Annals of Probability

- Ann. Probab.
- Volume 4, Number 1 (1976), 98-101.

### Prediction Theory and Ergodic Spectral Decompositions

#### Abstract

Linear prediction theory for a stationary sequence $X_n$ ordinarily begins with the assumption that the covariance $R(n) = E(X_{m + n} \bar{X}_m) = \int^\pi_{-\pi} e^{i\lambda n} dF(\lambda)$ is known. The best linear predictor of $X_0$ given the past $X_{-1}, X_{-2}, \cdots$ is then the projection $\psi$ of $X_0$ on the span of $X_{-1}, X_{-2}, \cdots$. The prediction error is $E(|X_0 - \psi|^2)$. In practice $R$ is not known but is estimated from the past. If the process is ergodic and the entire past is known this causes no problem since then the estimate $\hat{R}$ of $R$ must equal $R$. But if the process is not ergodic then $\hat{R}$ does not equal $R$. In this paper we consider the relationship between prediction using $\hat{R}$ and $R$. One conclusion is that if the process is Gaussian, it doesn't matter whether $\hat{R}$ or $R$ is used in constructing the best linear predictor. The predictor is the same and the prediction error is the same.

#### Article information

**Source**

Ann. Probab. Volume 4, Number 1 (1976), 98-101.

**Dates**

First available in Project Euclid: 19 April 2007

**Permanent link to this document**

https://projecteuclid.org/euclid.aop/1176996185

**Digital Object Identifier**

doi:10.1214/aop/1176996185

**Mathematical Reviews number (MathSciNet)**

MR391244

**Zentralblatt MATH identifier**

0337.60036

**JSTOR**

links.jstor.org

**Subjects**

Primary: 60G10: Stationary processes

Secondary: 60G15: Gaussian processes 60G25: Prediction theory [See also 62M20]

**Keywords**

Spectral decomposition linear prediction stationary sequences

#### Citation

Eisenberg, Bennett. Prediction Theory and Ergodic Spectral Decompositions. Ann. Probab. 4 (1976), no. 1, 98--101. doi:10.1214/aop/1176996185. https://projecteuclid.org/euclid.aop/1176996185