`findfrequency`

returns the period of the dominant frequency of a time
series. For seasonal data, it will return the seasonal period. For cyclic
data, it will return the average cycle length.

findfrequency(x)

## Arguments

x |
a numeric vector or time series of class `ts` |

## Value

an integer value

## Details

The dominant frequency is determined from a spectral analysis of the time
series. First, a linear trend is removed, then the spectral density function
is estimated from the best fitting autoregressive model (based on the AIC).
If there is a large (possibly local) maximum in the spectral density
function at frequency \(f\), then the function will return the period
\(1/f\) (rounded to the nearest integer). If no such dominant frequency
can be found, the function will return 1.

## Examples

findfrequency(USAccDeaths) # Monthly data

#> [1] 12

findfrequency(taylor) # Half-hourly data

#> [1] 48

findfrequency(lynx) # Annual data

#> [1] 10