I think the user should know better.
--------------------------------------------------
From: "Richard Hennessy" <rich.hennessy at verizon.net>
Sent: Wednesday, September 08, 2010 3:16 PM
To: "Dieter Kaiser" <drdieterkaiser at web.de>; "Raymond Toy" <toy.raymond at gmail.com>
Cc: <maxima at math.utexas.edu>
Subject: Re: [Maxima] inf - inf = 0 ??
> Infinity or inf or minf is an answer to a limit problem. It is not a number, so I think it makes no sense to fix it.
> No more sense than fixing this.
>
> (for i : 1 thru 6 do i : i+1) - (for j : 1 thru 6 do p);
>
> 0;
>
> Rich
>
> --------------------------------------------------
> From: "Dieter Kaiser" <drdieterkaiser at web.de>
> Sent: Wednesday, September 08, 2010 3:00 PM
> To: "Raymond Toy" <toy.raymond at gmail.com>
> Cc: <maxima at math.utexas.edu>
> Subject: Re: [Maxima] inf - inf = 0 ??
>
>> Am Dienstag, den 07.09.2010, 22:55 -0400 schrieb Raymond Toy:
>>> On 9/7/10 10:40 PM, Viktor T. Toth wrote:
>>> > Right now (testing with 5.21.0 and the current CVS), we have
>>> >
>>> > (%i3) limit(2/x-1/x,x,0);
>>> > (%o3) infinity
>>> >
>>> > but
>>> >
>>> > (%i6) limit(2/x,x,0)-limit(1/x,x,0);
>>> > (%o6) 0
>>> >
>>> > That just does not smell right.
>>> >
>>> > Shouldn't we have
>>> >
>>> > inf + inf = inf (NOT 2 inf),
>>> > inf - inf = und (NOT 0),
>>> > minf + minf = minf (NOT 2 minf),
>>> > minf - minf = und,
>>> > inf - minf = inf,
>>> > minf - inf = minf,
>>> > infinity + inf = infinity + minf = infinity + infinity = und,
>>> > infinity - inf = infinity - minf = infinity - infinity = und?
>>> I think these are all known bugs. I did some work on this but never
>>> finished it. I think Dieter has also done some work on this.
>>
>> Yes, I have done last year an implementation to simplify infinities. The
>> implementation worked well with the testsuite and share_testsuite.
>>
>> Unfortunately, I have lost this implementation. I had a problem with my
>> hard disk and no backup of the code. But it is not difficult to
>> implement it again. I only need some time.
>>
>> Dieter Kaiser
>>
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