Graphviz egde addition conundrum - graphviz

Question

I am trying to make images with Graphviz that will illustrate some process that involves adding a few edges to an existing graph. It is crucial that the vertices and edges of the base graph remain in place.
I've tried to add my new edges with [constraint=false] but keep getting different layouts for the base and the new graph, wherever I add more than one edge. Another method I tried with little to show for it was running dot for the graph with all the extra edges and then manually removing the extra lines - still no dice.
The graph I am trying to draw is this:
graph G{
overlap=scale;
node [weight=.2,height=.1];
edge [len=2.1];
3--2 [constraint=false];
4--1 [constraint=false];
5--3 [constraint=false];
6--1 ;
6--2 ;
6--3 ;
6--4 ;
6--5 ;
7--1 ;
7--2 ;
7--3 ;
7--4 ;
7--5 ;
8--1 ;
8--2 ;
8--3 ;
8--4 ;
8--5 ;
}
Any help will be greatly appreciated.

Answer 1

I think you can try with :
3--2 [style="invis"];
4--1 [style="invis"];
5--3 [style="invis"];
and then :
3--2 [style="bold"];
4--1 [style="bold"];
5--3 [style="bold"];
to show - and emphasis - the new edges.
The nodes and edges that are invis are not shown but still used to compute the layout.

Answer 2

Instead of Graphviz, there are many GUI graph analysis tools that let you run layout algorithms and position things manually. You can fix node positions, and even color or change the width the added edges to make them stand out. These tasks are trivial in NodeXL (C#), a great open source tool that integrates network analysis into Excel 2007/2010 (Disclaimer: I'm an advisor for it).
Here is your graph visualized in NodeXL, and another image with the new edges colored red.
To create the second image, just open up the 'Edges' worksheet in NodeXL and paste in your data in the first three columns like this:
3 2 red
4 1 red
5 3 red
6 1
6 2
6 3
6 4
6 5
7 1
7 2
7 3
7 4
7 5
8 1
8 2
8 3
8 4
8 5
You can download the graphml file here, which includes your data and the node coordinates that you could import into NodeXL.
There are tons of other open source GUI tools to visualize graphs, like Gephi (Java) and Cytoscape (Java), while Pajek, UCINet, yEd and Tom Sawyer are some proprietary alternatives.