Hi all,
There is indeed a bug in root(), but there seems to be an ambiguity
which needs to be solved: I think Luiz's command should give an error
for the reason I try to explain below.
As written in the help page, the option 'node' is an alternative to
'outgroup':
node: alternatively, a node number where to root the tree (this
should give the MRCA of the ingroup).
If the tree is unrooted, then at least 3 clades are connected to a
node (reminder: the tree is eventually unrooted before being
re-rooted) and thus there are several ways to define the in- and
outgroups (this is clear when plotting the tree with type = "u"). In
practice, this is not a problem since the action of root() is, by
default, to rearrange the edges in order to move 'node' at the base of
the tree when plotted by default.
If resolve.root = TRUE, then the in- and outgroups must be identified
more clearly:
If ‘resolve.root = TRUE’, ‘root’ adds a zero-length branch below
the MRCA of the ingroup.
So when the tree is plotted, the ingroup and the outgroup are
effectively sister-clades.
If 'node' is not the current root of the tree, the ambiguity is solved
arbitrarily by considering the clade on the right of 'node' (when the
tree is plotted by default) as the ingroup. So these (using Luiz's
tree) work:
root(t5, node = 7, resolve.root = TRUE)
root(t5, node = 8, resolve.root = TRUE)
Thus, I propose the following changes:
1)
root(phy, node = Ntip(phy) + 1, resolve.root = TRUE)
should return an explicit error.
2) The other cases of root(phy, node = ..., resolve.root = TRUE) may
still be allowed and the help page should be explicit about this.
I'm not certain about 2): to be consistent this should also return an
error, but maybe some users use this kind of commands (though I don't
think this is very common).
All comments welcome!
Best,
Emmanuel
Thu, 19 Mar 2015 15:37:47 -0400 "Liam J. Revell"
<liam.rev...@umb.edu>:
Maybe this is obvious, but even though your tree is unrooted, node 6
is the "root" of the edge matrix for the tree (i.e., it has the node
number equal to Ntip(tree)+1) - thus:
t5<-multi2di(t5)
will give you a resolved tree rooted at this node.
There seems to be a bug in root when you try to root an unrooted
tree at the "root" node (i.e., the node with node number
Ntip(tree)+1).
All the best, Liam
Liam J. Revell, Assistant Professor of Biology
University of Massachusetts Boston
web: http://faculty.umb.edu/liam.revell/
email: liam.rev...@umb.edu
blog: http://blog.phytools.org
On 3/19/2015 3:12 PM, Luiz Max Carvalho wrote:
Dear phylofolks,
I'm trying to root a tree on an internal (rather than a terminal)
branch.
Here is a small example:
library(ape)
t5 <- rmtree(N = 1, n = 5, rooted = FALSE)[[1]]
root(t5, node = 6, resolve.root = TRUE)
output: Error in if (i != N) { : argument is of length zero
root(t5, node = 7, resolve.root = TRUE)
output: Phylogenetic tree with 5 tips and 4 internal nodes.
Tip labels:
[1] "t4" "t3" "t2" "t5" "t1"
Rooted; includes branch lengths.
I don't understand why rooting at node 6 throws an error, while
using node
7 is fine. What am I missing?
Cheers,
Luiz
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