Re: [Maxima-discuss] float(exp(10000)) works, but float(exp(10000/3)) doesn't

[David S. <d.s...@go...>]

To clarify ... I'm generally fine with "float" failing for too large
numbers - that's why there is "bfloat" after all.

The original problem, which is now fixed by my patch, was that the
expression "abs(exp(10000/3)+1)" generated an error.

2016-01-26 17:32 GMT+01:00 Richard Fateman <fa...@be...>:
> On 1/26/2016 1:44 AM, David Scherfgen wrote:
>> Hello,
>>
>> I'm getting very weird and inconsistent behavior when doing
>> float(exp(10000)) vs. float(exp(10000/3)) and float(exp(10000.0)).
>>
>> The first one works - the result is promoted to bigfloat.
> This is a hack, and I suppose previously it overflowed.  float() used to
> convert to double-float machine
> precision.  Someone changed it to upgrade to bigfloat, i.e. make it the
> same as bfloat() when needed.
>
>> The second one gives me floating point infinity, even though the exp
>> argument is actually smaller!
> If you really want the number, try bfloat(exp(10000/3))  which works.
> Apparently the hack in
> the first example wasn't complete enough.
>> The third one gives an error.
> I think this one fails because exp(10000.0)  overflows  before float()
> sees it.
> Not a bug?
>
>>
>> I guess this is not intended, right?
>>
>> Maxima branch_5_37_base_407_g2af0c38 http://maxima.sourceforge.net
>> using Lisp GNU Common Lisp (GCL) GCL 2.6.12
>> Distributed under the GNU Public License. See the file COPYING.
>> Dedicated to the memory of William Schelter.
>> The function bug_report() provides bug reporting information.
>>
>> (%i1) float(exp(10000));
>> (%o1)                       8.806818225658306b4342
>>
>> (%i2) float(exp(10000/3));
>> (%o2)                               i.nfE+0
>>
>> (%i3) float(exp(10000.0));
>> float: floating point overflow converting 8.806818225662922b4342
>>   -- an error. To debug this try: debugmode(true);
>>
>> Best regards,
>> David Scherfgen
>>
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