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From: Doug Gregor (dgregor_at_[hidden])
Date: 2004-08-20 10:40:37

On Aug 20, 2004, at 9:22 AM, Gordon Smith wrote:

> Great thanks, this is working a lot better now...
> Comments (really just some boundary cases):
> 1. If two vertices have the same location before the layout is
> called, they
> will have the same location after the layout is finished.

Interesting. This case should probably be detected and the positions
perturbed slightly.

> 2. If _all_ the vertices have the same location, then there is an
> infinite
> loop (see 3).

I'm not entirely surprised... the above change could fix this.

> 3. I know you recommend calling circle_layout before calling the
> spring
> layout, but since this layout algorithm is very dependant on starting
> positions I think you will find this won't produce great results...
> In fact
> calling the spring algo several times in succession shows it gets
> "better"
> (in my project I animate the movement after each iteration), I will be
> playing with the "Done" rules over the next couple of days and will
> report
> back findings (if any are of interest).

The circular layout suggestion comes from Kamada & Kawai. If the
layouts aren't all that great, it's probably the fault of the "Done"
function object. Perhaps we need an absolute tolerance, or a tighter
relative tolerance, or even an iteration count... it's hard to know
what works well without a bit of testing.

> Again thanks for your work - I am comparing this spring layout against
> my
> spring layout and also against "neato" (which I can't animate) from the
> graphviz project.

Cool. I'd be interested to hear about the results.


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