mxAlgebra input

Hello,

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!