Ancestral graph
Check if it is an adjacency matrix of an ancestral graph
isAG(amat)
amat |
Checks if the following conditions must hold: (i) no undirected edge meets an arrowhead; (ii) no directed cycles; (iii) spouses cannot be ancestors. For details see Richardson and Spirtes (2002).
A logical value, TRUE if it is an ancestral graph and FALSE
otherwise.
Giovanni M. Marchetti, Mathias Drton
Richardson, T. S. and Spirtes, P. (2002). Ancestral Graph Markov Models. Annals of Statistics, 30(4), 962–1030.
## Examples from Richardson and Spirtes (2002) a1 <- makeMG(dg=DAG(a~b, b~d, d~c), bg=UG(~a*c)) isAG(a1) # Not an AG. (a2) p.969 a2 <- makeMG(dg=DAG(b ~ a, d~c), bg=UG(~a*c+c*b+b*d)) # Fig. 3 (b1) p.969 isAG(a2)
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