tree functions

[JuanPi]

Hi all,

The tree plotting function treeplot uses the predecessor list
description of a tree for plotting.
there is another representation of tree which is (I do not know the
formal name) based on the center node of the tree, it is usually more
compact than the predecessor list. It was described here[1].

I wrote a pair of functions to convert from one to the other[2,3] (up
to a relabeling of the nodes), it is quite simple, but I thought maybe
we can add it to Octave?

What would be the right place to put this functions? (they are not
documented yet, but if accepted I will do it, also I will write demos
and tests)

PS: I am planning to write the other algos in the paper, but I do not
know if those go into octave, probably not.

[1]: http://www.sciencedirect.com/science/article/pii/0012365X73900356
[2]: predecessors list to centered list:
https://bitbucket.org/KaKiLa/mymfiles/src/tip/pred2cent.m
[3]: centered list to predecessors list:
https://bitbucket.org/KaKiLa/mymfiles/src/tip/cent2pred.m


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JuanPi Carbajal
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