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

[Richard F. <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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