Returns the edge parameter of the two trees consistent with the speficied NNI rearrangement
DoubleNNI(parent, child, edgeToBreak)Integer vector corresponding to the first column of the edge
matrix of a tree of class phylo, i.e. tree$edge[, 1].
Integer vector corresponding to the second column of the edge
matrix of a tree of class phylo, i.e. tree$edge[, 2].
(optional) integer specifying the index of an edge to bisect/prune,
generated randomly if not specified.
Alternatively, set to -1 to return a complete list
of all trees one step from the input tree.
the tree$edge parameter of the two trees consistent with the specified rearrangement