On Saturday, March 30, 2019 at 2:56:59 AM UTC-7, Emmanuel Charpentier wrote:
>
> *TL;DR :* Sage can produce a symbolic expression :
>
> - that it can't evaluate numerically when correcly substiuted, AND
> - that can be evaluated when typed manually.
>
> The problem seems ti be bound to absolute values.
>
> That, IMHO, is a first-class bug...
>
> *Demonstation :* I think that some results produced by fricas' integrator
> are wrong, and wanted to show it numerically.
>
> It suggests that somehow the fricas interface returned an expression that
prints like something usable, but isn't. It looks like this can mess with
the state of SR to break things more permanently:
sage: SR("abs(1)").n()
1.00000000000000
sage: sage.symbolic.function_factory.function('abs')(1).n()
TypeError: cannot evaluate symbolic expression numerically
sage: SR("abs(1)").n()
TypeError: cannot evaluate symbolic expression numerically
sage: abs(1)
1
I suspect that the fricas interface has a dictionary entry missing and
hence creates a new symbolic function for something that can otherwise be
evaluated. My bet would be the fricas interface needs some work. But that's
an optional component, so the number of people testing that and/or willing
to work on that will be relatively low. Looks ticket-worthy though.
Workaround: don't use the fricas interface.
Disclaimer: I haven't reproduced or tested anything with fricas so my
analysis may be way off.
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