\HeaderA{glm.control}{Auxiliary for Controlling GLM Fitting}{glm.control}
\keyword{optimize}{glm.control}
\keyword{models}{glm.control}
\begin{Description}\relax
Auxiliary function as user interface for \code{\LinkA{glm}{glm}} fitting.
Typically only used when calling \code{\LinkA{glm}{glm}} or \code{\LinkA{glm.fit}{glm.fit}}.
\end{Description}
\begin{Usage}
\begin{verbatim}
glm.control(epsilon = 1e-8, maxit = 25, trace = FALSE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{epsilon}] positive convergence tolerance \eqn{\epsilon}{};
the iterations converge when
\eqn{|dev - dev_{old}|/(|dev| + 0.1) < \epsilon}{|dev - devold|/(|dev| + 0.1) < \epsilon}.
\item[\code{maxit}] integer giving the maximal number of IWLS iterations.
\item[\code{trace}] logical indicating if output should be produced for each
iteration.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
If \code{epsilon} is small, it is also used as the tolerance for the
least squares solution.

When \code{trace} is true, calls to \code{\LinkA{cat}{cat}} produce the
output for each IWLS iteration. Hence, \code{\LinkA{options}{options}(digits = *)}
can be used to increase the precision, see the example.
\end{Details}
\begin{Value}
A list with the arguments as components.
\end{Value}
\begin{References}\relax
Hastie, T. J. and Pregibon, D. (1992)
\emph{Generalized linear models.}
Chapter 6 of \emph{Statistical Models in S}
eds J. M. Chambers and T. J. Hastie, Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{glm.fit}{glm.fit}}, the fitting procedure used by
\code{\LinkA{glm}{glm}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
### A variation on  example(glm) :

## Annette Dobson's example ...
counts <- c(18,17,15,20,10,20,25,13,12)
outcome <- gl(3,1,9)
treatment <- gl(3,3)
oo <- options(digits = 12) # to see more when tracing :
glm.D93X <- glm(counts ~ outcome + treatment, family=poisson(),
                trace = TRUE, epsilon = 1e-14)
options(oo)
coef(glm.D93X) # the last two are closer to 0 than in ?glm's  glm.D93
# put less so than in R < 1.8.0 when the default was 1e-4
\end{ExampleCode}
\end{Examples}

