This method returns the n × n covariance matrix of the noise variables in the Gaussian graphical model. The diagonal in this matrix consists of the indeterminates p(i,i). Each off-diagonal entry is zero unless there is a bidirected edge between i and j in which case the corresponding entry in the matrix is the indeterminate p(i,j). The documentation of gaussianRing further describes the indeterminates p(i,j).
i1 : G = mixedGraph(digraph {{b,{c,d}},{c,{d}}},bigraph {{a,d}})
o1 = MixedGraph{Bigraph => Bigraph{a => set {d}} }
d => set {a}
Digraph => Digraph{b => set {c, d}}
c => set {d}
d => set {}
Graph => Graph{}
o1 : MixedGraph
|
i2 : R = gaussianRing G o2 = R o2 : PolynomialRing |
i3 : compactMatrixForm =false; |
i4 : bidirectedEdgesMatrix R
o4 = | p 0 0 p |
| a,a a,d |
| |
| 0 p 0 0 |
| b,b |
| |
| 0 0 p 0 |
| c,c |
| |
| p 0 0 p |
| a,d d,d |
4 4
o4 : Matrix R <--- R
|