Returned matrices (expCov, expMean, A,S, etc) only reflect last row of data

You are correct that the returned values of a matrix or algebra that depends upon a definition variable will only reflect the values of that definition variable in the last row of the dataset. I doubt that was a deliberate design decision. Instead, the matrix or algebra simply retains the last value it held during the run. Keep in mind that definition variables, as their name implies, define the specific statistical model applied to each row of the dataset. In other words, the model for each row is defined conditional on its values of the definition variables. In general, every row could have different values of the definition variables, meaning that a slightly different model would be applied to each row. Many times, one or more free parameters will represent how much certain quantities change as a function of the definition variables. An easy example is conditioning the expected means on the definition variables via linear regression; the tell-tale parameters in this case would be the regression coefficients.

Could you further describe the behavior you'd prefer to see from OpenMx in this regard?

Hi Charles,

It is a design feature to leave the matrices and algebras at their last computed state. You're right that it is general to any model, not just RAM models. Definition variables could be used for many things in many different ways . Thus, OpenMx does not presume to know how you might want matrices or algebras printed. We just leave them in their last computed form. A weighted combination might make sense for your use case, but be meaningless or misleading in others' cases.

The summary() function gives you a nice report of the estimated parameters. And mxEval() can be used to get the computed form of any matrix or algebra for any row of data.


AModel <- mxmodel(...)
ARun <- mxRun(AModel) #Model with definition variables
mxEval(AMatrixOrAlgebra, model=ARun, compute=TRUE, defvar.row=14)
# result/values of AMatrixOrAlgebra from model ARun at definition variable row 14.