\name{ParameterObject}
\alias{ParameterObject}
\alias{NullParameter}
\alias{pvec}
\alias{pvec<-}
\title{A generic parameter for a proficiency or evidence model}
\description{

  This is a generic representation for a parameter set for either a
  \code{\link{ProficiencyModel}} or an \code{\link{EvidenceModel}}.
  The actual details will vary with the implementation.  Usually
  parameter objects are designed to work with a specific proficiency or
  evidence model.
}
\usage{
ParameterObject(...)
pvec(param)
pvec(param) <- value
NullParameter()
}
\arguments{
  \item{\dots}{
    These will depend on the implementing class, usually the various
    parameters.
  }
  \item{param}{A \code{ParameterObject} whose parameters are to be accessed.}
  \item{value}{A numeric vector containing the new parameters.}
}
\details{

  Generally the details of this object type are given by the
  implementation.  See the Subclasses below.

  The method \code{pvec} returns all of the parameters as a single
  vector.  This is used for optimization routines.

  The \code{NullParameter} object is a special parameter to be used when
  a placeholder for a parameter to be supplied later is needed.
  
}
\value{

  \code{ParameterObject()} would return an object of type
  \code{ParameterObject}, but it does not work as \code{ParameterObject}
  is an abstract class.

  \code{NullParameter()} returns an object of type \code{NullParameter}.

  The generic function \code{pvec} returns the parameters in vectorized form.
  
}
\references{
%% ~put references to the literature/web site here ~
}
\author{Russell Almond}
\seealso{

  Instances:

  \code{NullParameter}, \code{\link{TimelessNormalParam}}.

  Contained By:
  \code{\link{AbstractModel}}

}
\examples{
  np <- NullParameter()
  stopifnot(is(np,"ParameterObject"))
  ## Abstract class, see TimelessNormalParam for an example.
}
\keyword{ class }