If you SHOW AS TEXT, you can cut and paste to save in a file of your choosing (and edit it as you choose). You can load such a file with the "Load from file" function. (The LOAD and SAVE functions use cookies, with a nonstandard encoding to reduce their size.) Good question about perfect computation with rationals. There are an awful lot of square roots in the calculations; I'm not sure the conditions under which they don't produce irrationals. I suspect one dimensional scenarios are more likely to be able to produce exact results. (It's been a long time since I looked at this code. I do remember deliberately not adding in gravity because that made reversibility harder. The PDP-6 version had gravity. And I vaguely remember having some code to make sure energy was [nearly] conserved, but I'm not sure it's in this new version.) --ms On 12-Nov-16 01:44, Bill Gosper wrote:

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Date: 2016-11-05 09:51 From: Mike Speciner <ms@alum.mit.edu> https://ms0.github.io/gas.html This is a great toy! I delete everything except six identical balls (and maybe one wall), set one ball to bounce around for a while before disrupting the others, run it half a minute into the disruption, save it out, and show it time-reversed to some unsuspecting person. Or if I'm afraid they'll notice the negative time passage, I manually negate all the velocities before saving. (Is there a way to load one of those text files?)

Unfortunately, neither of these reversal stunts is perfect, due to accumulated numerical errors, which I assume you've worked hard to minimize.

So let's get particularly math-y and ask: Given rational positions and velocities, can we simulate one of these six-ball scenarios exactly and indefinitely, without runaway denominator buildup, nor irrational collision results? --rwg _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun