[GiNaC-list] Ordering of expressions

Richard B. Kreckel kreckel at ginac.de
Mon Aug 10 23:06:30 CEST 2009

Burcin Erocal wrote:
> In order to use ginac as the symbolics backend in Sage [1], we also had
> to work around this random printing problem.

May I ask why stable printing is a requirement for use in Sage?

> In retrospect, this was not the right way to fix the printing problem.
> I should have done as the ginac developers suggested when I first asked
> about this [2]. Unfortunately, I didn't know much about the design of
> the ginac library then, and I wanted to get things done quickly.
> [2] http://www.ginac.de/pipermail/ginac-list/2008-August/001406.html
> When I find the time, I plan to move the new comparison functions out
> of the way and bring back the old ones to make things fast again. Then,
> add some code in expairseq to sort its arguments with the new
> comparison functions before printing, and cache the sorted sequence
> somewhere. I don't expect to have the time to do this in the near
> future however.
> I hope some of this will be useful if you try to stabilize printing
> order in ginac.

It won't be difficult to sort terms lexicographically, when printing, as 
opposed to based on hash values. But I doubt that caching the sorted 
sequence will be of practical use.

Richard B. Kreckel

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