fix.family.link {mgcv} | R Documentation |
Generalized Additive Model fitting by `outer' iteration, requires extra derivatives of the variance and link functions to be added to family objects. The functions add what is needed.
fix.family.link(fam) fix.family.var(fam)
fam |
A family . |
Outer iteration GAM estimation requires derivatives of the GCV/UBRE score, which are obtained by differentiating the P-IRLS GAM fitting iteration w.r.t. the model smoothing parameters. The expressions for the derivatives require the second derivative of the link w.r.t. the mean, and the first derivative of the variance function w.r.t. the mean. These functions add functions evaluating these quantities to a family.
If the family already has functions dvar
and d2link
then these
functions simply return the family unmodified: this allows non-standard links
to be used with gam
when using outer iteration (performance
iteration operates with unmodified families).
The dvar
function is a function of a mean vector, mu
, and returns
a vector of corresponding first derivatives of the family variance
function. The d2link
function is also a function of a vector of mean
values, mu
: it returns a vector of second derivatives of the link,
evaluated at mu
.
If modifying your own family, note that you can often get away with supplying
only a dvar
function if your family only requires links that occur in
one of the standard families.
A family object with extra component functions dvar
and d2link
.
Simon N. Wood simon.wood@r-project.org