Definition Variables

[brandmaier]

Does the package support definition variables as in OpenMx? If not, I strongly vote for including this in both the package and Stenograph.
If this is not yet, implemented, it should either just be a symbol within fixed(...) which is then interpreted as a column name from which the data is read out, or it could be a new modifier defvar(...) that takes a symbol as input.

[brandmaier]

I just want to bump this issue up because I find it important, @aaronpeikert

I believe that definition variables are easy to add in StructuralEquationModels.jl but I understand that StenoGraph.jl needs a generic way to specify them, which may be harder to come up with.

For definition variables, we need a simple wrapper that takes a Symbol corresponding to a variable name (e.g. escaped by defvar(...) in a dataset, then create a multi-group model, in which each person have their own model, all parameters are set to equality across model and the definition variable is set to fixed at a value that the model has to get from the dataset. This should be relatively easy, right?

[aaronpeikert]

From stenographs point of view definition variables are normal nodes with some modifier indicating they are definition variables so this should be trivial!