# Internal Functions Dealing with `hhh4`

Models

`hhh4_internals.Rd`

The functions documented here are considered *internal*,
i.e., not intended to be called by the user. They are used by
add-on packages dealing with `hhh4`

models.

## Usage

```
meanHHH(theta, model, subset = model$subset, total.only = FALSE)
sizeHHH(theta, model, subset = model$subset)
decompose.hhh4(x, coefs = x$coefficients, ...)
```

## Arguments

- theta,coefs
numeric vector of

*untransformed*model parameters, i.e., the`coefficients`

element of the`"hhh4"`

object.- model
the model terms as returned by the

`terms`

-method for`"hhh4"`

objects.- subset
vector of time points for which to compute the component means. Defaults to the fitted time range. For

`sizeHHH`

,`subset=NULL`

means to return the vector of dispersion parameters.- total.only
logical. Should only the total mean (epidemic + endemic) be returned in a

`length(subset)`

x nUnit matrix? Otherwise, a list of such matrices is returned, giving the values of the various model components separately (as well as the total).- x
a fitted

`hhh4`

model.- ...
unused.

## Details

`meanHHH`

computes the components of the mean returned in
`length(subset)`

x nUnit matrices.
`sizeHHH`

computes the model dispersion in `dnbinom`

(`mu`

, `size`

) parametrization (it returns `NULL`

in
the Poisson case).
`decompose.hhh4`

decomposes the fitted mean (extracted via
`meanHHH`

) in an array with dimensions \((t, i, j)\), where the
first \(j\) index is `"endemic"`

.