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% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/MxCompute.R
\name{mxComputeEM}
\alias{mxComputeEM}
\alias{MxComputeEM-class}
\title{Fit a model using DLR's (1977) Expectation-Maximization (EM) algorithm}
\usage{
mxComputeEM(
expectation = NULL,
predict = NA_character_,
mstep,
observedFit = "fitfunction",
...,
maxIter = 500L,
tolerance = 1e-09,
verbose = 0L,
freeSet = NA_character_,
accel = "varadhan2008",
information = NA_character_,
infoArgs = list(),
estep = NULL
)
}
\arguments{
\item{expectation}{a vector of expectation names \lifecycle{deprecated}}
\item{predict}{what to predict from the observed data \lifecycle{deprecated}}
\item{mstep}{a compute plan to optimize the completed data model}
\item{observedFit}{the name of the observed data fit function (defaults to "fitfunction")}
\item{...}{Not used. Forces remaining arguments to be specified by name.}
\item{maxIter}{maximum number of iterations}
\item{tolerance}{optimization is considered converged when the maximum relative change in fit is less than tolerance}
\item{verbose}{integer. Level of run-time diagnostic output. Set to zero to disable}
\item{freeSet}{names of matrices containing free variables}
\item{accel}{name of acceleration method ("varadhan2008" or "ramsay1975")}
\item{information}{name of information matrix approximation method}
\item{infoArgs}{arguments to control the information matrix method}
\item{estep}{a compute plan to perform the expectation step}
}
\description{
The EM algorithm constitutes the following steps: Start with an
initial parameter vector. Predict the missing data to form a
completed data model. Optimize the completed data model to obtain
a new parameter vector. Repeat these steps until convergence
criteria are met.
}
\details{
The arguments to this function have evolved. The old style
\code{mxComputeEM(e,p,mstep=m)} is equivalent to the new style
\code{mxComputeEM(estep=mxComputeOnce(e,p), mstep=m)}. This change
allows the API to more closely match the literature on the E-M
method. You might use \code{mxAlgebra(..., recompute='onDemand')} to
contain the results of the E-step and then cause this algebra to
be recomputed using \code{mxComputeOnce}.
This compute plan does not work with any and all expectations. It
requires a special kind of expectation that can predict its
missing data to create a completed data model.
The EM algorithm does not produce a parameter covariance matrix
for standard errors. The Oakes (1999) direct method and S-EM, an
implementation of Meng & Rubin (1991), are included.
Ramsay (1975) was recommended in Bock, Gibbons, & Muraki (1988).
}
\examples{
library(OpenMx)
set.seed(190127)
N <- 200
x <- matrix(c(rnorm(N/2,0,1),
rnorm(N/2,3,1)),ncol=1,dimnames=list(NULL,"x"))
data4mx <- mxData(observed=x,type="raw")
class1 <- mxModel("Class1",
mxMatrix(type="Full",nrow=1,ncol=1,free=TRUE,values=0,name="Mu"),
mxMatrix(type="Full",nrow=1,ncol=1,free=TRUE,values=4,name="Sigma"),
mxExpectationNormal(covariance="Sigma",means="Mu",dimnames="x"),
mxFitFunctionML(vector=TRUE))
class2 <- mxRename(class1, "Class2")
mm <- mxModel(
"Mixture", data4mx, class1, class2,
mxAlgebra((1-Posteriors) * Class1.fitfunction, name="PL1"),
mxAlgebra(Posteriors * Class2.fitfunction, name="PL2"),
mxAlgebra(PL1 + PL2, name="PL"),
mxAlgebra(PL2 / PL, recompute='onDemand',
initial=matrix(runif(N,.4,.6), nrow=N, ncol = 1), name="Posteriors"),
mxAlgebra(-2*sum(log(PL)), name="FF"),
mxFitFunctionAlgebra(algebra="FF"),
mxComputeEM(
estep=mxComputeOnce("Mixture.Posteriors"),
mstep=mxComputeGradientDescent(fitfunction="Mixture.fitfunction")))
mm <- mxOption(mm, "Max minutes", 1/20) # remove this line to find optimum
mmfit <- mxRun(mm)
summary(mmfit)
}
\references{
Bock, R. D., Gibbons, R., & Muraki, E. (1988). Full-information
item factor analysis. \emph{Applied Psychological Measurement,
6}(4), 431-444.
Dempster, A. P., Laird, N. M., & Rubin, D. B. (1977). Maximum likelihood from
incomplete data via the EM algorithm. \emph{Journal of the Royal Statistical Society.
Series B (Methodological)}, 1-38.
Meng, X.-L. & Rubin, D. B. (1991). Using EM to obtain asymptotic variance-covariance
matrices: The SEM algorithm. \emph{Journal of the American Statistical Association,
86} (416), 899-909.
Oakes, D. (1999). Direct calculation of the information matrix via
the EM algorithm. \emph{Journal of the Royal Statistical Society:
Series B (Statistical Methodology), 61}(2), 479-482.
Ramsay, J. O. (1975). Solving implicit equations in psychometric data analysis.
\emph{Psychometrika, 40} (3), 337-360.
Varadhan, R. & Roland, C. (2008). Simple and globally convergent
methods for accelerating the convergence of any EM
algorithm. \emph{Scandinavian Journal of Statistics, 35}, 335-353.
}
\seealso{
\link[=mxAlgebra]{MxAlgebra}, \link{mxComputeOnce}
}
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