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 => {d}} } d => {a} Digraph => Digraph{b => {c, d}} c => {d} d => {} 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 |