gaussianRing G
This function creates a polynomial ring in the indeterminates $s_{(i,j)}$ associated to the covariance matrix of the model plus two new lists of indeterminates:
 The $l_{(i,j)}$ indeterminates consist of regression coefficients associated to the directed edges in the graph.
 The $p_{(i,j)}$ indeterminates in the gaussianRing are the nonzero entries in the covariance matrix of the error terms in the graphical model associated to a mixed graph with bidirected edges.
Note that since version 2.0 of the package, gaussianRing of a directed graph is built as a gaussianRing of a mixed graph with only directed edges, see gaussianRing(MixedGraph).





