Hi Julien, On Sun, 06 Feb 2011 09:30:16 +0100 Julien PUYDT <julien.pu...@laposte.net> wrote:
> Le 05/02/2011 11:44, Francois Bissey a écrit : > > So gamma could be called from C, Cython, possibly mpmath, pynac or > > maxima. I guess you could tests the results calling from mpmath or > > maxima. I am guessing that SR(10.0r).gamma() will end up being a > > call to maxima to compute gamma but I could be completely off > > track. But since it is also a gamma computation it could be related > > to the previous computation of gamma(6). On most platforms, we use the tgammal() function provided by the C library to evaluate gamma when the input is a float. See lines 1032-1039 of sage/symbolic/pynac.pyx and 21-28 of sage/symbolic/pynac_cc.h for the relevant code. > Here are a few computations : > > sage: gamma(6.) > 120.000000000000 Here 6. is a RealLiteral. This gets converted to a RealNumber with the default precision. Then the evaluation is done with the .gamma() method of real numbers, which uses MPFR. sage: type(6.) <type 'sage.rings.real_mpfr.RealLiteral'> > sage: gamma(float(6)) > 119.99999999999997 > sage: SR(6.0r).gamma() > 119.99999999999997 Both these examples call the same code in sage/symbolic/pynac.pyx I mentioned above and pass the evaluation to the C library. The cephes library was included in the standard Sage distribution recently to prevent these problems, but some symbolic functions still need to switch to using that when the C library is unreliable. The file sage/symbolic/pynac_cc.h is there to facilitate this switch. > Launching, from my sage directory : > LD_LIBRARY_PATH=./local/lib ./local/bin/maxima > > I can write : > (%i1) gamma(6.); > (%o1) 120 > (%i2) gamma(6.0000000000000000000000); > (%o2) 120.0 Using maxima for such things would be incredibly slow. We avoid that when possible. But, as you can see from the comments in sage/symbolic/pynac.pyx, the special functions in Sage, especially those provided by GiNaC/pynac need a lot of work. Thank you. 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
