Login

News

Set starting values

Posted on
Picture of user. icha Joined: 03/13/2014
Forums
General SEM Discussions
I want to ask what exactly the purpose of setting the starting value in mxPath codes? And what the basic can we use to set it? Is it like trial and error? I set some values but it always generate the NaN value in standard error, so what should I do then? Thank you.
Replied on Tue, 03/25/2014 - 09:51
Picture of user. tbates Joined: 07/31/2009

hi icha,

This thread will likely help with explanations and some practical advice.

http://openmx.psyc.virginia.edu/thread/1366

you might want to explore the umx library, which has a umxSetValues() function which takes some "usually good enough" guesses at start values.

it's on github rather than cran at present so installing means


install.packages("devtools")
library("devtools")
devtools::install_github("tbates/umx")
library("umx")
# then have a look at
help(umxStart)

Log in or register to post comments
Replied on Wed, 03/26/2014 - 02:18
Picture of user. icha Joined: 03/13/2014

I've installed devtools package and also umx package but when I run help(umxSetValues) I've got an error,why? And I want to ask what makes the standar error NaN? Is it just based on the starting values? I've tried some starting values and it always result the NaN values in my standar error.Thankyou
Log in or register to post comments
Replied on Wed, 03/26/2014 - 06:40
Picture of user. tbates Joined: 07/31/2009

Sorry, spoke without code :-) Here's a working example from the umx help

In general, I'd recommend reading Ryne's post on setting values and learning to do that directly as well as using utility helpers like this one...


require(OpenMx)
data(demoOneFactor)
require(OpenMx)
data(demoOneFactor)
latents = c("G")
manifests = names(demoOneFactor)
m1 <- mxModel("One Factor", type = "RAM",
manifestVars = manifests, latentVars = latents,
mxPath(from = latents, to = manifests),
mxPath(from = manifests, arrows = 2),
mxPath(from = latents, arrows = 2, free = F, values = 1.0),
mxData(cov(demoOneFactor), type = "cov", numObs = 500)
)
m1 = umxStart(m1) # some likely guess entered for model means, variances and covariances
# You can also set labels automatically:
umxGetParameters(m1) # Only "matrix address" labels: "One Factor.S[2,2]" "One Factor.S[3,3]"
m1 = umxLabel(m1)
umxGetParameters(m1, free = T) # now all labeled regularly "G_to_x1", "x4_with_x4", etc.

This is a shortcut to both using umxRun()

m1 = umxRun(m1, setLabels= T, setValues=T)

Log in or register to post comments
  Login

News