At 06:01 PM 11/13/01 -0500, Bagotronix Tech Support wrote:
>Since a complex board has many
>constraints, the router's choices are limited to alternatives it is capable
>of deciding between.  A wider open board presents the router with too many
>alternatives, which it's limited judgement cannot decide between wisely.
>That's my theory, anyway.

Very funny. :-) On the off chance Mr. Baggett was serious:

Too bad the router does not know *wisely* from a hole in a ground plane.

Where routers have more than one option, they typically take the first one 
discovered, or they search for more than one option and then score each one 
according to programmed cost parameters to choose the one to take. If two 
options are equivalent, they just choose the first one.

It is important that router behavior be reproducible. I would use a 
pseudo-random generator from a user-input seed to choose between equally 
costed choices, that would provide some flexibility while maintaining 
reproducibility. You really could run the router many times with different 
seeds, finding the one which worked best.

The router routes small boards *very* quickly, so the "infinity of options" 
theory simply does not hold water.

>The AR3 router could be coaxed to provide acceptable results if you tried
>many different options and rules until you found the "right" mix.

I think most of the user-accessible rules were taken out....

>Fortunately, AR3 was so fast that you could try things out and quickly
>determine if they were going to work.  That big job I mentioned was routed
>to 100% completion in 44 minutes, as I recall, after I spent all day
>"tweaking" it in trial runs.

The Router is very good when it works, decent when it is marginal, and 
sometimes it just can't handle the task. But I've done some boards where I 
prerouted some difficult areas and then let the router complete the easy stuff.

But the autorouter is only one small reason to upgrade from v. 3 among many 
others. Too bad we did not have this conversation several months ago or 
better several years ago, it would have been cheaper and you would have 
known why we are giving you this advice.

Abdulrahman Lomax
Easthampton, Massachusetts USA

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