[Numpy-discussion] Bug in logaddexp2.reduce

Anne Archibald peridot.faceted@gmail....
Thu Apr 1 00:46:12 CDT 2010


On 1 April 2010 01:40, Charles R Harris <charlesr.harris@gmail.com> wrote:
>
>
> On Wed, Mar 31, 2010 at 11:25 PM, <josef.pktd@gmail.com> wrote:
>>
>> On Thu, Apr 1, 2010 at 1:22 AM,  <josef.pktd@gmail.com> wrote:
>> > On Thu, Apr 1, 2010 at 1:17 AM, Charles R Harris
>> > <charlesr.harris@gmail.com> wrote:
>> >>
>> >>
>> >> On Wed, Mar 31, 2010 at 6:08 PM, <josef.pktd@gmail.com> wrote:
>> >>>
>> >>> On Wed, Mar 31, 2010 at 7:37 PM, Warren Weckesser
>> >>> <warren.weckesser@enthought.com> wrote:
>> >>> > T J wrote:
>> >>> >> On Wed, Mar 31, 2010 at 1:21 PM, Charles R Harris
>> >>> >> <charlesr.harris@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


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