Re: [Maxima-discuss] bugs related to infinity ?

[Stavros M. (Σ. Μ. <mac...@al...>]

​Agreed that it is not a perfect fix. But "the best is the enemy of the
good".

              -s​


On Sun, Jun 29, 2014 at 1:40 AM, Richard Fateman <fa...@be...>
wrote:

> These are not fixes. At best they move the bugs/features.  The failure
> remains as
> a failure in referential transparency because of the transfinite numbers.
>
> Let's define   f(x):= x^2/x.
>
> Maxima simplifies  f(z) to   z.
>
> For all z.
>
>
> except this is a lie for some values of z that one can imagine, like
> inf, und, minf,  and
> (depending on how you define them)  intervals.
>
> so if you choose to do arithmetic on infs, most of the rest of the
> system becomes broken.
>
> Inf (etc) are not numbers.  They are handy notations for limits and
> such.  But patches such
> as making 0*inf be und  will not work unless you simplify  0*x to   "if
> transfinite(x) then und else 0"
> or some such thing.
>
> RJF
>
>
>
> On 6/28/2014 4:31 PM, Robert Dodier wrote:
> > On 2014-06-28, Dimiter Prodanov <dim...@gm...> wrote:
> >
> >>>> 0*minf
> >> 0
> >> should be undefined
> >>
> >>>>   0*inf
> >> 0
> >> should be undefined
> >>
> >>>> 0*infinity;
> >> 0
> >> should be undefined
> > I agree that these are all bugs and we should simplify such expressions
> > as suggested.
> >
> >> On the other hand, in Non-Standard analysis/ Infinitesimal calculus the
> >> results can be OK.
> > Maxima had better stick to standard analysis -- heaven knows we have
> > enough trouble as it is ....
> >
> > best
> >
> > Robert Dodier
> >
> >
> >
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