```
# This is the undirected graphical model from Edwards (2000).
data(marks)
ug = empty.graph(names(marks))
arcs(ug, check.cycles = FALSE) = matrix(
c("MECH", "VECT", "MECH", "ALG", "VECT", "MECH", "VECT", "ALG",
"ALG", "MECH", "ALG", "VECT", "ALG", "ANL", "ALG", "STAT",
"ANL", "ALG", "ANL", "STAT", "STAT", "ALG", "STAT", "ANL"),
ncol = 2, byrow = TRUE,
dimnames = list(c(), c("from", "to")))
```

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