Tim Bates

Probably want @mhunter1 eyes on this as it touches mxRefModels

https://github.com/OpenMx/OpenMx/pull/352

Correct way to graph an algebra on a path would be: ```R mxPath("x", to="y", formula= b1*x+b2*def) ``` 

Hey Mike: your idea works! Be nice to have algebra on a path, and to not have to manually create the dummy var, but this gets moderation working, and expands...

This paper on ML-SEM? Mehta, P. D., & Neale, M. C. (2005). People are variables too: multilevel structural equations modeling. _Psychol Methods_, **10**, 259-284. doi:10.1037/1082-989X.10.3.259 [pdf](https://www.statmodel.com/download/mehtaneale.PDF)

re: "_Is it not possible to label a path as a definition variable in RAM? I would be surprised to see this lack of functionality_" Were you meaning that we...

Changes to implement: 1. `mxPath` gains a `formula` parameter, which takes an algebra (equivalent to expression 2. RAM gains a n*1 "D" matrix which stores parameters (mostly equivalent to diamonds...

Instead of passing the formula through it ends up as the symbol `expression` Any clues on how to pass the formula on? ```R newPath

Great to see movement on this issue. An algebra, however, doesn't create the path . If I'm wrong, I'd like to see an example of such an algebra implementing, say,...

One very intuitive method for scripting this model would be ```R mxModel( mxPath("z", "y") mxPath("x", "y", ) mxPath(x*z, "y") # allow formula input to the `from` parameter. ) ``` Slightly...