This function reroots a phylogenetic tree with respect to the
specified outgroup.
Usage
root(phy, outgroup)
Arguments
phy
an object of class "phylo".
outgroup
a vector of mode numeric or character specifying the tips
to delete.
Value
an object of class "phylo".
Details
The argument outgroup can be either character or numeric. In
the first case, it gives the labels of the tips to be deleted; in the
second case the numbers of these labels in the vector
phy$tip.label are given.
If outgroup is of length one (i.e. a single value), then the
tree is rerooted using the node below this tip as the new root.
If outgroup is of length two or more, the most recent common
ancestor (MRCA) is used as the new root. Note that the tree is really
unrooted before being rerooted, so that if outgroup is already
the outgroup, then the returned tree is not the same than the original
one (see examples). If outgroup is not monophyletic, the
operation fails and an error message is issued.