mxAlgebra input

for a SEM model I have calculated the expected covariance matrix using the symbolic linear algebra functionalities of the `Ryacas` package. To use the expected covariance matrix to calculate some second order statistics, I'm wondering whether the `mxAlgebra` function accepts some sort of R objects/expressions? Or does it only accept the "raw" names of the `mxMatrix` objects? I'm grateful for any hint on the topic.
Thanks!