optimizers: sem Optimizers

In sem: Structural Equation Models

sem Optimizers

Description

The default optimizer used by sem is optimizerSem, which employs compiled code and is integrated with the objectiveML and objectiveGLS objective functions; optimizerSem, written by Zhenghua Nie, is a modified version of the standard R nlm optimizer, which was written by Saikat DebRoy, R-core, and Richard H. Jones. The other functions call optimizers (nlm, optim, or nlminb), to fit structural equation models, and are called by the sem function. The user would not normally call these functions directly, but rather supply one of them in the optimizer argument to sem. Users may also write them own optimizer functions. msemOptimizerNlm is for fitting multigroup models, and also adapts the nlm code.

Usage

optimizerSem(start, objective=objectiveML,  
	gradient=TRUE, maxiter, debug, par.size, model.description, warn, ...)
	
optimizerMsem(start, objective=msemObjectiveML, gradient=TRUE,
	maxiter, debug, par.size, model.description, warn=FALSE, ...)
	
optimizerNlm(start, objective=objectiveML, gradient=TRUE, 
	maxiter, debug, par.size, model.description, warn, ...)
	
optimizerOptim(start, objective=objectiveML, gradient=TRUE, 
	maxiter, debug, par.size, model.description, warn, method="CG", ...)

optimizerNlminb(start, objective=objectiveML, gradient=TRUE, maxiter, 
	debug, par.size, model.description, warn, ...)

msemOptimizerNlm(start, objective=msemObjectiveML, gradient=TRUE,
		maxiter, debug, par.size, model.description, warn=FALSE, ...)

Arguments

start	a vector of start values for the parameters.
objective	the objective function to be optimized; see objective.functions.
gradient	TRUE if an analytic gradient is to be used (if one is available).
maxiter	the maximum number of iterations allowed.
debug	TRUE to show the iteration history and other available information about the optimization.
par.size	"startvalues" to have the optimizer scale the problem according to the magitudes of the start values (ignored by optimizerNlminb).
model.description	a list with elements describing the structural-equation model (see the code for details).
warn	if FALSE, suppress warnings during the optimization.
method	the method to be employed by the optim optimizer; the default is "CG" (conjugate-gradient).
...	additional arguments for the nlm, optim, or nlminb optimizer.

Value

An object of class "semResult", with elements:

convergence	TRUE if the optimization apparently converged.
iterations	the number of iterations required.
par	the vector of parameter estimates.
vcov	the estimated covariance matrix of the parameter estimates, based on a numeric Hessian; not supplied by optimizerNlminb.
criterion	the optimized value of the objective function.
C	the model-implied covariance or moment matrix at the parameter estimates.
A	the estimated A matrix.
P	the estimated P matrix.

Author(s)

John Fox [e-mail], and Zhenghua Nie, in part adapting work by Saikat DebRoy, R-core, and Richard H. Jones.

See Also

sem, objective.functions, nlm, optim, nlminb

sem documentation built on Sept. 12, 2024, 7:39 a.m.