On Mon, 14 Mar 2011 17:40:41 +0100 Julien PUYDT <julien.pu...@laposte.net> wrote:
> Le 14/03/2011 14:12, David Kirkby a écrit : > > > > On 14 March 2011 13:04, David Kirkby<david.kir...@onetel.net> > > wrote: > >> On 13 March 2011 15:34, Julien PUYDT<julien.pu...@laposte.net> > >> wrote: > >>> Hi, > >>> > >>> among the few failing tests with my ARM built, two are because of > >>> accuracy reasons : > >>> > >>> File > >>> "/home/jpuydt/sage-4.6.2/devel/sage/sage/functions/other.py", > >>> line 497: sage: gamma1(float(6)) Expected: > >>> 120.0 > >>> Got: > >>> 119.99999999999997 <snip> > >>> File > >>> "/home/jpuydt/sage-4.6.2/devel/sage/sage/symbolic/expression.pyx", > >>> line 6067: sage: SR(10.0r).gamma() > >>> Expected: > >>> 362880.0 > >>> Got: > >>> 362880.00000000047 <snip> > > > > Perhaps you can find value of n, such that gamma(n) gives an exact > > integer result. If that happens on other CPUs too, then I suggest > > the argument to the doctest is changed. > > The solution of finding a "good" integer is fragile : it will break > anytime wind will change direction. > > Actually, the best solution is the one I gave : handle fuzzy results! > You have to keep in mind that floats can't seriously be used for > equality -- there is a margin of error (and the margin moves > according to the floating comma which gave its name to the type). > > Are doctests pure string checks? Can't they allow things like > "(result - expected) < 0.0000001" ? The doctests are pure string checks. You can explicitly check that the error is less than a certain value as John Palmieri wrote in another response, but in this case, we should fix the real problem and make sure our gamma() function returns correct results. On many platforms, the tgammal() function from the c library gives results with adequate precision. However, on some, like cygwin [1] or ARM, this is not the case. We should call a different function to compute gamma for floating point input on these platforms. [1] http://trac.sagemath.org/sage_trac/ticket/9162 This can be done by changing the relevant lines in sage/symbolic/pynac_cc.h. Perhaps the gsl_sf_gamma() from GSL [2] or something from cephes [3] will do the job. [2] http://www.gnu.org/software/gsl/manual/html_node/Gamma-Functions.html [3] http://www.netlib.org/cephes/ Cheers, Burcin -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
