Actually they're all consistant if you use float('inf') instead of oo.
Aaron Meurer
On Sun, Apr 7, 2013 at 5:28 PM, Aaron Meurer <asmeu...@gmail.com> wrote:
> 0**0 follows Python conventions. The rest are likely equally useful.
>
> By the way, 0*oo does give nan as it should.
>
> Aaron Meurer
>
> On Apr 7, 2013, at 4:59 PM, "hacm...@gmail.com" <hacm...@gmail.com> wrote:
>
> Why are the indeterminate forms oo/oo, 0/0, and oo-oo recognized as nan, but
> not 1**oo, 0**0, 0*oo, oo**0?
>
> On Sunday, April 7, 2013 2:38:14 PM UTC-4, Aaron Meurer wrote:
>>
>> That's because subs just works dumbly, so it produces (1 + 1/oo)**oo,
>> which gives 1**oo, which gives 1. A limit procedure doesn't fall into
>> this trap because it knows that 1**oo is an indeterminate form (for
>> exactly this reason). We could probably "fix" this by making 1**oo
>> give nan, but that would no doubt break a ton of other stuff.
>>
>> I really think that we should scrap these limit heursitics. They have
>> lead to dozens of wrong results like this one, where limit() is wrong,
>> but gruntz() is right. The whole point of limit() is that you can't
>> trust subs, so the fact that limit() uses subs is contradictory. And
>> the ironic thing is that limit() doesn't always return the result when
>> subs does (for example, limit() on Piecewise gives
>> NotImplementedError), hence workarounds like the one in
>> Expr._eval_interval.
>>
>> Aaron Meurer
>>
>>
>> On Sun, Apr 7, 2013 at 12:21 PM, Ankit Agrawal <aaaag...@gmail.com> wrote:
>> >
>> >
>> >
>> >
>> > On Sunday, April 7, 2013 11:25:11 PM UTC+5:30, Sergey Kirpichev wrote:
>> >>
>> >> Yes. This is a bug in the limit() heuristic.
>> >>
>> >>
>> >> gruntz() works well:
>> >> In [5]: from sympy.series import gruntz
>> >> In [6]: gruntz(1+(1+1/x)**x,x,oo)
>> >> Out[6]: 1 + ℯ
>> >>
>> > Yes. I tried to narrow down the root of the bug and it is in _sift() at
>> > line
>> > 188 of series.limits in current master.
>> > It is actually the .subs that generates value of 1 for on (1 + 1/a)**a
>> >
>> >>>> ((1 + 1/a)**a).subs(a,oo)
>> > 1
>> >
>> > --
>> > You received this message because you are subscribed to the Google
>> > Groups
>> > "sympy" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> > an
>> > email to sympy+un...@googlegroups.com.
>> > To post to this group, send email to sy...@googlegroups.com.
>> > Visit this group at http://groups.google.com/group/sympy?hl=en-US.
>> > For more options, visit https://groups.google.com/groups/opt_out.
>> >
>> >
>
> --
> You received this message because you are subscribed to the Google Groups
> "sympy" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to sympy+unsubscr...@googlegroups.com.
> To post to this group, send email to sympy@googlegroups.com.
> Visit this group at http://groups.google.com/group/sympy?hl=en-US.
> For more options, visit https://groups.google.com/groups/opt_out.
>
>
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sympy+unsubscr...@googlegroups.com.
To post to this group, send email to sympy@googlegroups.com.
Visit this group at http://groups.google.com/group/sympy?hl=en-US.
For more options, visit https://groups.google.com/groups/opt_out.
