This README describes the constraint Fruchterman Reingold
layout algorithm.

As the name indicate this algorithm is based on the spring-
embedder algorithm proposed by THOMAS M. J. FRUCHTERMAN
and EDWARD M. REINGOLD. (Software-Practice and Experience,
Vol 21(11) 1129-1164 (November 1991).
It is enhanced to solve given constraints. Therefore
some additional forces, checks and heuristics were added.

Graphs SHOULD be directed in order to use constraints.
The algorithm works with undirected graphs as well,
but you are not able to 'see' the direction of the
constraints. The simulation treats all 'normal' edges
as undirected edges. 

To describe constraints you may specify edgelabel as 
combinations of the following characters:

'r':		right
'l':		left
'a' 'o':	above (oberhalb von)
'b' 'u':	below (unterhalb von)
'v':		vertical alignment (same x-coordinate)
'h':		horizontal alignment (same y-coordinate)
'*':		this edge just describes a constraint and
		is not part of the 'real' graph. Therefore
		it will be ingnored during the simulation.
number >= 1	any number >= 1 in the label will be interpreted as
		a group identifier for uniform edgelengths-groups.
		A label like "777 3 lr" indicates that this edge
		belongs to both groups 777 and 3. So these groups
		will be joined to one group.

To make things easier you may also specify nodelabels.
A nodelabel is added to all adjacent edges. 
This can be confusing if you don't take care of the
direction of the edges. So some special characters
are allowed for nodelabels:

'A' 'O':	place this node above all of its neighbours
'B' 'U':	place this node below all of its neighbours
'R':		place this node on the right of its neightbours
'L':		place this node on the left of its neightbours

To seperate the real node/edge comments from the constraints
you may specify arbitray delimiters. The default is ','

If you specify unsolvable constraints the algorithm
you will get an error message. Additionally some
nodes will be coloured to give you some hints
where to look for the errors.

After the layout nodes will be coloured according to
the remaining forces at the end of the simulation.
The most tense node will be colored red. Then the 
scheme goes down from black to white, which indicates 
just a low force at the nodes. The level of the remaining
forces must be considered if you want to interpret 
these colors.



