The R Project SVN R-packages

% File nlme/man/simulate.lme.Rd
% Part of the nlme package for R
% Distributed under GPL 2 or later: see nlme/LICENCE.note

\name{simulate.lme}
\title{Simulate Results from \code{lme} Models}
\alias{simulate.lme}
\alias{plot.simulate.lme}   % currently undocumented (needs own help page)
\alias{print.simulate.lme}
\usage{
\method{simulate}{lme}(object, nsim = 1, seed = , m2,
         method = c("REML", "ML"), niterEM = c(40, 200), useGen, \dots)
}
\arguments{
  \item{object}{
    an object inheriting from class \code{"\link{lme}"}, representing a fitted
    linear mixed-effects model, or a list containing an \code{lme} model
    specification.  If given as a list, it should contain
    components \code{fixed}, \code{data}, and \code{random}
    with values suitable for a call to \code{\link{lme}}.  This argument
    defines the null model.
  }
  \item{m2}{an \code{"\link{lme}"} object or a list, like \code{object}
    containing a second lme model specification.  This argument defines
    the alternative model.  If given as a list, only those parts of the
    specification that change between model \code{object} and \code{m2}
    need to be specified.}
  \item{seed}{
    an optional integer that is passed to \code{set.seed}.  Defaults to
    a random integer.
  }
  \item{method}{an optional character array.  If it includes
    \code{"REML"} the models are fit by maximizing the restricted
    log-likelihood.  If it includes \code{"ML"} the log-likelihood is
    maximized.  Defaults to \code{c("REML", "ML")}, in which case both
    methods are used.}
  \item{nsim}{an optional positive integer specifying the number of
    simulations to perform.  Defaults to \code{1}. \bold{This has
      changed.  Previously the default was 1000.}
  }
  \item{niterEM}{an optional integer vector of length 2 giving the number of
    iterations of the EM algorithm to apply when fitting the \code{object}
    and \code{m2} to each simulated set of data.  Defaults to \code{c(40,200)}.
  }
  \item{useGen}{
    an optional logical value.  If \code{TRUE}, the \code{\link{nlminb}}
    optimizer is used with numerical derivatives of the log-likelihood. If
    \code{FALSE}, the \code{\link{nlm}} algorithm is used with an
    analytic gradient.  The default
    depends on the \code{"\link{pdMat}"} classes used in \code{object} and \code{m2}:
    if both are standard classes (see \code{\link{pdClasses}}) then
    defaults to \code{FALSE}, otherwise defaults to \code{TRUE}.
  }
  \item{\dots}{optional additional arguments.  None are used.}
}
\description{
  The model \code{object} is fit to the data.  Using
  the fitted values of the parameters, \code{nsim} new data vectors from
  this model are simulated.  Both \code{object} and \code{m2} are fit by
  maximum likelihood (ML) and/or by restricted maximum likelihood (REML)
  to each of the simulated data vectors.
}
\value{
  an object of class \code{simulate.lme} with components \code{null} and
  \code{alt}.  Each of these has components \code{ML} and/or \code{REML}
  which are matrices.  An attribute called \code{seed} contains
  the seed that was used for the random number generator.
}
\references{
  Pinheiro, J.C., and Bates, D.M. (2000)
  \emph{Mixed-Effects Models in S and S-PLUS}, Springer.
}
\author{José Pinheiro and Douglas Bates \email{bates@stat.wisc.edu}}
\seealso{\code{\link{lme}}, \code{\link{set.seed}}}
\examples{
orthSim <-
   simulate.lme(list(fixed = distance ~ age, data = Orthodont,
                     random = ~ 1 | Subject),
                nsim = 3, # limited here for speed
                m2 = list(random = ~ age | Subject))
% checked in ../tests/predict.lme.R
}
\keyword{models}