gaussianRing G
This function accepts a mixed graph as input. The outputted ring contains the indeterminates $s_{(i,j)}$ associated to the covariance matrix of the model plus two or three new lists of indeterminates depending on the type of edges of the graph:
- The $k_{(i,j)}$ indeterminates in the gaussianRing are the nonzero entries in the concentration matrix in the graphical model associated to the undirected graph.
- 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.
Mixed graphs in this package can be of two different types depending on their edges:
Directed and bidirected edges: two new lists of indeterminates. For each directed edge $i \to j$ in the mixed graph there is an indeterminate, denoted by default $l_{(i,j)}$, corresponding to the associated direct causal effect parameter in the model. For each bidirected edge $i$<->$j$ there is an indeterminate, denoted by default $p_{(i,j)}$, corresponding to the associated noise parameter. Finally, for each node $i$, there is an indeterminate $p_{(i,i)}$.
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Undirected, directed and bidirected edges: three new lists of indeterminates. Besides the two already described above, undirected edges are dealt with in the same way as in gaussianRing applied to a graph, with the corresponding indeterminates being $k_{(i,j)}$ by default.
Only loopless mixed graphs are accepted and they must have a vertex ordering compatible with partitionLMG. For more details about loopless mixed graphs, see the paper: Kayvan Sadeghi and Steffen Lauritzen, Markov properties for mixed graphs, Bernoulli, 20 (2014), no 2, 676-696.
Be aware that several functions in this package that accept mixed graphs are still not implemented for mixed graphs with undirected edges: gaussianParametrization, gaussianVanishingIdeal, trekIdeal, trekSeparation, identifyParameters.
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