[Numpy-discussion] Bug in logaddexp2.reduce

[Anne Archibald]

On 1 April 2010 01:40, Charles R Harris <charlesr.harris at gmail.com> wrote:
>
>
> On Wed, Mar 31, 2010 at 11:25 PM, <josef.pktd at gmail.com> wrote:
>>
>> On Thu, Apr 1, 2010 at 1:22 AM,  <josef.pktd at gmail.com> wrote:
>> > On Thu, Apr 1, 2010 at 1:17 AM, Charles R Harris
>> > <charlesr.harris at gmail.com> wrote:
>> >>
>> >>
>> >> On Wed, Mar 31, 2010 at 6:08 PM, <josef.pktd at gmail.com> wrote:
>> >>>
>> >>> On Wed, Mar 31, 2010 at 7:37 PM, Warren Weckesser
>> >>> <warren.weckesser at enthought.com> wrote:
>> >>> > T J wrote:
>> >>> >> On Wed, Mar 31, 2010 at 1:21 PM, Charles R Harris
>> >>> >> <charlesr.harris at gmail.com> wrote:
>> >>> >>
>> >>> >>> Looks like roundoff error.
>> >>> >>>
>> >>> >>>
>> >>> >>
>> >>> >> So this is "expected" behavior?
>> >>> >>
>> >>> >> In [1]: np.logaddexp2(-1.5849625007211563, -53.584962500721154)
>> >>> >> Out[1]: -1.5849625007211561
>> >>> >>
>> >>> >> In [2]: np.logaddexp2(-0.5849625007211563, -53.584962500721154)
>> >>> >> Out[2]: nan
>> >>> >>
>> >>> >
>> >>> > Is any able to reproduce this?  I don't get 'nan' in either 1.4.0 or
>> >>> > 2.0.0.dev8313 (32 bit Mac OSX).  In an earlier email T J reported
>> >>> > using
>> >>> > 1.5.0.dev8106.
>> >>>
>> >>>
>> >>>
>> >>> >>> np.logaddexp2(-0.5849625007211563, -53.584962500721154)
>> >>> nan
>> >>> >>> np.logaddexp2(-1.5849625007211563, -53.584962500721154)
>> >>> -1.5849625007211561
>> >>>
>> >>> >>> np.version.version
>> >>> '1.4.0'
>> >>>
>> >>> WindowsXP 32
>> >>>
>> >>
>> >> What compiler? Mingw?
>> >
>> > yes, mingw 3.4.5. , official binaries release 1.4.0 by David
>>
>> sse2 Pentium M
>>
>
> Can you try the exp2/log2 functions with the problem data and see if
> something goes wrong?

Works fine for me.

If it helps clarify things, the difference between the two problem
input values is exactly 53 (and that's what logaddexp2 does an exp2
of); so I can provide a simpler example:

In [23]: np.logaddexp2(0, -53)
Out[23]: nan

Of course, for me it fails in both orders.

Anne