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The purpose of mxEval() is to allow you to evaluate arbitrary R statements which may include data from inside a model.
mxEval() takes two essential parameters: the statement you want to evaluate, and a model in which to look for objects.
Optionally, you can include "compute=TRUE" to evaluate an OpenMx statement using R and "show=TRUE" to show where how mxEval translated your statement into full references to R and model objects
The simplest and most common use of mxEval is to extract a matrix from a model:
mxEval(M, model)
--> matrix M from model
note: If M is not found in the model, but an object called M exists in your R environment, mxEval will return that object. To avoid misleading results, use full object names, for instance, if the name of model is "model", this statement will only return M if model.M exists
mxEval(model.M, model)
--> matrix M from model
To refer to objects in submodels, use the submodel name
mxEval(mz.M+ dz.M, model)
--> sum of 'M' matrices found in submodels mz and dz
You can also do algebra and arithmetic inside mxEval, so this works:
mxEval(2 %x% M, model)
--> 2.M