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Revision of omxGraphviz help (making path diagrams) from Wed, 02/08/2012 - 13:30

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Wiki home pageOpenMx can output path diagrams using the dot syntax.

You can learn about this language for describing path diagrams at several online tutorials.

The R for generating a path diagram from a model is straightforward:

     omxGraphviz(model, dotFilename="")

(currently for RAM models only)

If you leave parameter 2 blank, the dot file will be output into the R console.

There's a complete example:

manifests <- names(demoOneFactor)
latents <- c("G1")
model1 <- 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)
omxGraphviz(model1, "")

Rendering the output

dot output is in simple text file describing the latent and manifest variables (nodes) and their connections (edges) of a diagram.

To visualise the diagram, this .dot script must be processed by an application such as graphvis.

Other programmes that can open .dot include Omnigraffle.

This app does a nice job of rendering .dot

This site has an online renderer, which is handy for cut and paste: Paste this in to see a sex lim model :-)

t1 [label="Pt1", shape=box]
t2 [label="Pt2", shape=box]

Af -> Am [dir=both, label="ag"]
Cf -> Cm [dir=both, label="eta"]

Af -> t1 [label="af"]
Cf -> t1 [label="cf"]
Ef -> t1 [label="ef"]

Am -> t2 [label="am"]
Cm -> t2 [label="cm"]
Em -> t2 [label="em"]

{rank=min; Af; Cf; Ef; Am; Cm; Em; }; {rank=max; t1; t2}; Escorts Amsterdam


The example on this page:
omxGraphviz(model, dotFileName="")
should be
omxGraphviz(model, dotFilename="")
(i.e., "Name" written as "name"), otherwise R does not understand it.
- Kimmo