README contains 3 sections

1) How to compile make the merger tree code
2) How to make use of the code
3) The Format used to store the tree

Note:  This code was updated on 13th November 2007.  Prior to that
the split_PCH.F90 algorithm had a small error. After correcting the
error we redid the fits and got slightly different parameters.
The version of the paper stating the correct parameter values 
and corresponding plots is that published in MNRAS and version 3 on astro-ph.
The new parameters are correctly set in trees.F90 .


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1) How to compile make the merger tree code
============================================

Code.tar.gz  -- contains all the code, Makefile and data
                files you need.

Download Code.tar.gz and unpack using 
      gunzip Code.tar.gz
      tar xvf Code.tar

Edit the first lines in the Makefile to point to your favoured F90 compiler
and to select the compiler flags you require


Compile the code using
       make trees.exe


This should compile all the code and create an executable, trees.exe,
which when run should produce output similar to:

The redshifts at which the tree will be stored:
z=  0.000 at which deltcrit= 1.674
z=  0.444 at which deltcrit= 2.075
z=  0.889 at which deltcrit= 2.544
z=  1.333 at which deltcrit= 3.051
z=  1.778 at which deltcrit= 3.578
z=  2.222 at which deltcrit= 4.117
z=  2.667 at which deltcrit= 4.662
z=  3.111 at which deltcrit= 5.212
z=  3.556 at which deltcrit= 5.765
z=  4.000 at which deltcrit= 6.318
main storage=     7.4 Mbytes
make_tree(): internal storage =   0.025 Mbytes
internal halo tree storage=   0.050 Mbytes
internal halo tree storage=   0.099 Mbytes
internal halo tree storage=   0.198 Mbytes
 made a tree 1
 Counting the number of nodes in the tree.
number of nodes in tree  1 is      130230
 Example information from the tree:
 Base node:
   mass= 1.0E+14  z=  0.0E+0  number of progenitors  4399
 First progenitor:
   mass= 6.822631E+13  z=  0.44444441
   mass= 1.5742615E+13  z=  0.44444441
 made a tree 2
 Counting the number of nodes in the tree.
number of nodes in tree  2 is      131346
 Example information from the tree:
 Base node:
   mass= 1.0E+14  z=  0.0E+0  number of progenitors  4400
 First progenitor:
   mass= 8.3043544E+13  z=  0.44444441
   mass= 1.2592812E+12  z=  0.44444441


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2) How to make use of the code
==============================

The program trees.f90 that you compiled above is just an example
code. It sets up all the cosmological and other parameters that
the trees depend upon, it generates a tree, counts the number
of the nodes in the tree, outputs some information on the first
three nodes in the tree and repeats this for a second tree before stopping.

To do something useful with the code you could insert calls to you
own routines in place of the code that simply counts the number of nodes.
 

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3) The Format used to store the tree
====================================

The tree itself is stored in the array MergerTree .
This is an array of tree nodes each is of the "defined type"
TreeNode that is defined in defined_types.F90
This means that each node has the components 

%mhalo  -- mass of the progenitor halo
%jlevel -- indicates the halo exists a the redshift corresponding to
           expansion factor alev(jlevel)
%nchild -- the number of progenitors of children this halo has
%parent -- pointer to node that is the parent (descendant) of this halo
%child -- pointer to node that is the first child (most massive progenitor) 
           of this halo
%sibling --pointer to node the next most massive sibling of this halo
           (next most massive progenitor halo that shares the same 
            descendent halo)

There are also other components that used in the GALFORM code, but
undefined in these simple dark matter trees.


An example of walking around the tree is given by the code in
trees.F90 that counts the number of nodes in the tree.
It uses the function Walk_Tree() to walk around the tree
and there are other useful routines of this nature in the
file tree_routines.F90.