This is some functions for Pari/GP making calculations on labelled oriented trees and forests (graph theory trees) as "vpar" vector of parent vertex numbers. Functions include
Vertices are numbered 1 to n. A tree is a vector "
vpar[v] is parent of
0 if no
parent. Such a representation is oriented in that there is a distinguished
root (or roots for a forest) and labelled in that each vertex has a particular
number. There are no other attributes etc.
3 ^ ^ tree, root=3 / \ 1 5 vpar=[3,1,0,1,3] ^ ^ / \ 2 4
The main use is to calculate or verify properties of specific trees of interest. Various functions like diameter are the same for any root or labelling so effectively act as on a "free" tree and the vertex numbers just for tree creation. Most functions are linear in the number of vertices so can be used on large trees.
Connections to Pari/GP things include polynomials for roots (spectra),
matrices for some linear algebra,
Set()s for independent sets,
permutations in relabelling, and then general compactness of GP for
vpar.gp(652k, and sig), or compressed
vpar-14.tar.gz(806k, and sig)
vpar.gp is enough to run. Comments at the start give an
introduction and overview. The
tar file includes some example
scripts, self-tests, and work-in-progress extras. The extras mostly work but
may change wildly. The sig files are Gnu
PG ascii armoured signatures generated from my
The examples include bits of
gentreeg in the
Nauty tools which can generate
free trees in vertex parent form, and other forms, and can be used command
line or C.
for other graph (and tree) creation in Perl.
This page Copyright 2017, 2018, 2019 Kevin Ryde, except for the GPLv3 logo which is Copyright Free Software Foundation and used here in accordance with its terms.
(Back to the sitemap, or the Pari/GP section there).