Case when umxAlgebra fails

[lf-araujo]

Dear Tim,

I tried to find the culprit myself, but failed. There is a situation where umxAlgebra is failing:

regModel     <- mxModel("Regression101",
  mxData(observed = Twins2a_1, type = "raw"),
  umxMatrix("residualVar", type = "Full", nrow = 1, ncol = 1, free = TRUE, 
                          values = 10, labels = 'resid'),
  umxMatrix("Intercept", type="Full", nrow=1, ncol=1, free=TRUE, values=50,
                labels="beta0T1"),
  umxMatrix("bSite", type = "Full", nrow=1, ncol=1, free=TRUE, values=1,
                labels="beta1T1"),
  umxMatrix("Site", type="Full", nrow=1, ncol=1, free=FALSE,
               labels="data.Site_T1"),
  mxAlgebra(name = "regress", Intercept + bSite%x%Site),
  mxExpectationNormal(covariance="residualVar", 
                                    means="regress",
                                    dimnames=depVar ),
  mxFitFunctionML())

In the case above the model runs as expected, however when changing the line:

  umxAlgebra(name = "regress", Intercept + bSite%x%Site),

Then I get:

Error: Unknown reference 'expression' detected in the entity 'regress' in model 'Regression101'

[tbates]

I never got umxAlgebra working: something non-transparent happens that breaks passing the expression parameter to mxAlgebra - the word expression gets interpreted and broken.... I think mxAlgebra is doing things in a non-standard way, and I could not find a way via expression or match.call or do.call to get it passed along...

I thought I had added a "don't use help" message,: added now.

Happy to solve this with you, but unless the OpenMx people can suggest sometthing: probably should just delete the function :-( ...