# spectrum0.ar

0th

Percentile

##### Estimate spectral density at zero

The spectral density at frequency zero is estimated by fitting an autoregressive model. spectrum0(x)/length(x) estimates the variance of mean(x).

Keywords
ts
##### Usage
spectrum0.ar(x)
x
A time series.
##### Details

The ar() function to fit an autoregressive model to the time series x. For multivariate time series, separate models are fitted for each column. The value of the spectral density at zero is then given by a well-known formula.

##### Value

• A list with the following values
• specThe predicted value of the spectral density at frequency zero.
• orderThe order of the fitted model

##### Note

The definition of the spectral density used here differs from that used by spec.pgram. We consider the frequency range to be between 0 and 0.5, not between 0 and frequency(x)/2.

spectrum, spectrum0, glm.