specials: Special functions used in ssm formulas
In ClausDethlefsen/sspir: State Space Models in R

Description Usage Arguments Details Author(s) See Also Examples

Auxiliary function for modelling the time-dependent trend patterns when formulating ssm models.

polytrig(time, period = 365.25, degree = 1)
polytime(time, degree = 1)
sumseason(time, period = 12)
season(time, period = 12)

`time`	a vector giving the observation times, eg. `1:n`. The variable 'time' is by default set to `time(y)`, where `y` is the response in the formula in the `ssm` call.
`period`	the period of the seasonal pattern.
`degree`	the degree of the trigonometric polynomial or the degree of the polynomial time trend.

polytrig defines a trigonometric polynomial in time, polytime defines a polynomial time trend, sumseason produces a seasonal pattern in which the factors sum to zero over the period, and season defines a factor. The functions polytrig and season can be used outside the ssm call. However, polytime and sumseason are treated mainly inside the ssm call.