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Subject: Re: [geda-user] Apollon
From: John Doty <jpd AT noqsi DOT com>
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Date: Sun, 13 Sep 2015 20:03:01 -0600
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On Sep 13, 2015, at 7:38 PM, DJ Delorie <dj AT delorie DOT com> wrote:

> 
> So... internally *every* value is a fraction?

Yep.

>  I imagine integer
> overflow might be a non-trivial problem to solve.

Not one you need to worry about in a language that supports rationals. I use rationals in Mathematica all the time: floating point is poison to complicated algebra. The techniques are well know and efficient, although not as efficient as floating point hardware.

> 
> But if the whole point is to defer imprecise operations, what is the
> advantage of this over just storing the angles as degrees and doing
> the math on the fly?

The problem is that you’ll accumulate error when you have both rotations and translations.

>  Just speed?  /me wonders what the speed
> difference would be, if you include all the division ops you've
> created a need for,

Huh? Division of rationals is easy.

> plus algorithms to find pythagorean triples as
> needed,

Have a table. Or use Euclid’s formula (https://en.wikipedia.org/wiki/Pythagorean_triple#Generating_a_triple).

> plus overflow protection of a sort, etc.

Taken care of automatically if you choose a suitable language.

> 
> I'm not even sure we've covered all the advantages of storing
> rotations as a relationship rather than a transformation... like, if
> we "down symbol" we'd want to edit the unrotated symbol.
> 

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com