On Wed, Mar 31, 2010 at 11:46 PM, Anne Archibald <peridot.face...@gmail.com>wrote:
> On 1 April 2010 01:40, Charles R Harris <charlesr.har...@gmail.com> wrote: > > > > > > On Wed, Mar 31, 2010 at 11:25 PM, <josef.p...@gmail.com> wrote: > >> > >> On Thu, Apr 1, 2010 at 1:22 AM, <josef.p...@gmail.com> wrote: > >> > On Thu, Apr 1, 2010 at 1:17 AM, Charles R Harris > >> > <charlesr.har...@gmail.com> wrote: > >> >> > >> >> > >> >> On Wed, Mar 31, 2010 at 6:08 PM, <josef.p...@gmail.com> wrote: > >> >>> > >> >>> On Wed, Mar 31, 2010 at 7:37 PM, Warren Weckesser > >> >>> <warren.weckes...@enthought.com> wrote: > >> >>> > T J wrote: > >> >>> >> On Wed, Mar 31, 2010 at 1:21 PM, Charles R Harris > >> >>> >> <charlesr.har...@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. > > Ah, that's progress then ;) The effective number of bits in a double is 53 (52 + implicit bit). That shouldn't cause problems but it sure looks suspicious. Chuck
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