a character(1); when comprising "p" the name of
each node with its parents are given, when comprising "r" the formula regression
of each node is given with the node, when comprising "m" the model is given.
digits
when not null, the number of digits for rounding.
ordering
Nodes are given following the indices of "ordering"
if numeric or the names if it is character. NULL
means the identity permutation. Repetitions or missing nodes are
accepted.
chk
Check of the consistency of 'nbn' be performed before printing.