On Thu, Jun 02, 2011 at 04:17:19PM +0100, Garth N. Wells wrote: > > > On 02/06/11 16:05, Anders Logg wrote: > > On Thu, Jun 02, 2011 at 03:53:18PM +0100, Garth N. Wells wrote: > >> > >> > >> On 02/06/11 15:52, Anders Logg wrote: > >>> On Thu, Jun 02, 2011 at 03:31:31PM +0100, Garth N. Wells wrote: > >>>> > >>>> > >>>> On 02/06/11 15:21, Benjamin Kehlet wrote: > >>>>> On 2 June 2011 14:59, Garth N. Wells <gn...@cam.ac.uk> wrote: > >>>>>> > >>>>>> > >>>>>> On 02/06/11 12:10, Benjamin Kehlet wrote: > >>>>>>> On 2 June 2011 11:51, Anders Logg <l...@simula.no> wrote: > >>>>>>>> On Thu, Jun 02, 2011 at 10:46:29AM +0100, Garth N. Wells wrote: > >>>>>>>>> > >>>>>>>>> > >>>>>>>>> On 02/06/11 10:26, Anders Logg wrote: > >>>>>>>>>> On Thu, Jun 02, 2011 at 10:07:59AM +0100, Garth N. Wells wrote: > >>>>>>>>>>> > >>>>>>>>>>> > >>>>>>>>>>> On 01/06/11 23:46, Anders Logg wrote: > >>>>>>>>>>>> Have you checked that there is no performance penalty? > >>>>>>>>>>> > >>>>>>>>>>> I just have - evaluating a Legendgre polynomial 10k times at the > >>>>>>>>>>> same > >>>>>>>>>>> point is just noise with both methods (of the order 10^-5 - 10^-4 > >>>>>>>>>>> s). > >>>>>>>>>> > >>>>>>>>>> It may be noise for some applications, but not for others. I'm not > >>>>>>>>>> sure this is a bottle-neck for the ODE code (Benjamin will know) > >>>>>>>>>> but > >>>>>>>>>> we need to evaluate Legendre polynomials of degree > 100 many times > >>>>>>>>>> and then it may not be noise. > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> For very high degree (e.g. 200) Boost is marginally faster. > >>>>>>>> > >>>>>>>> Sounds promising then. > >>>>>>>> > >>>>>>>>>>> The Boost code is slightly slower because it doesn't cache the > >>>>>>>>>>> values > >>>>>>>>>>> (which is nice not to do), but may be faster if the call is > >>>>>>>>>>> inlined. > >>>>>>>>>>> It's not possible to inline it at the moment because of clashes > >>>>>>>>>>> between > >>>>>>>>>>> tr1:tuple and boost::tuple (Boost bug, I suspect). Old and new > >>>>>>>>>>> are the > >>>>>>>>>>> same when evaluating at different points. > >>>>>>>>>> > >>>>>>>>>> Let's wait for Benjamin to comment. > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> The speed is about the same (with scope to improve the speed for > >>>>>>>>> Boost) > >>>>>>>>> for unique values. The caller should be responsible for caching, if > >>>>>>>>> desired, since it can lead to memory blow out. > >>>>>>>>> > >>>>>>>>> Legendre does not appear in the ode code. It only appears in the > >>>>>>>>> computation of quadrature schemes. > >>>>>>>> > >>>>>>>> True, but the quadrature schemes are used in the ode code. > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>>> Garth > >>>>>>>>> > >>>>>>>>> > >>>>>>>>> > >>>>>>>>>>> Garth > >>>>>>>>>>> > >>>>>>>>>>> > >>>>>>>>>>>> Benjamin has > >>>>>>>>>>>> worked quite hard on optimizing some of the basic math routines > >>>>>>>>>>>> (in > >>>>>>>>>>>> some cases by many many orders of magnitude). > >>>>>>>>>>>> > >>>>>>>>>>>> Benjamin, can you take a look that it still works? > >>>>>>> > >>>>>>> Yes, the performance seems to be about the same, but I'm unable to > >>>>>>> compile it with support for GMP. > >>>>>>> > >>>>>>> /usr/include/boost/math/special_functions/legendre.hpp:178: > >>>>>>> instantiated from ‘typename boost::math::tools::promote_args<RT, > >>>>>>> float, float, float, float, float>::type boost::math::legendre_p(int, > >>>>>>> int, T, const Policy&) [with T = __gmp_expr<__mpf_struct [1], > >>>>>>> __mpf_struct [1]>, Policy = > >>>>>>> boost::math::policies::policy<boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy, > >>>>>>> boost::math::policies::default_policy>]’ > >>>>>>> /usr/include/boost/math/special_functions/legendre.hpp:185: > >>>>>>> instantiated from ‘typename boost::math::tools::promote_args<RT, > >>>>>>> float, float, float, float, float>::type boost::math::legendre_p(int, > >>>>>>> int, T) [with T = __gmp_expr<__mpf_struct [1], __mpf_struct [1]>]’ > >>>>>>> /home/benjamik/fenics/dolfin-wells_gmp/dolfin/math/Legendre.cpp:42: > >>>>>>> instantiated from here > >>>>>>> /usr/include/boost/math/special_functions/legendre.hpp:167: error: no > >>>>>>> matching function for call to ‘pow(__gmp_expr<__mpf_struct [1], > >>>>>>> __gmp_binary_expr<long int, __gmp_expr<__mpf_struct [1], > >>>>>>> __gmp_binary_expr<__gmp_expr<__mpf_struct [1], __mpf_struct [1]>, > >>>>>>> __gmp_expr<__mpf_struct [1], __mpf_struct [1]>, > >>>>>>> __gmp_binary_multiplies> >, __gmp_binary_minus> >, > >>>>>>> __gmp_expr<__mpf_struct [1], __gmp_binary_expr<__gmp_expr<__mpf_struct > >>>>>>> [1], __mpf_struct [1]>, long int, __gmp_binary_divides> >)’ > >>>>>>> /usr/include/bits/mathcalls.h:154: note: candidates are: double > >>>>>>> pow(double, double) > >>>>>>> /usr/include/c++/4.4/cmath:358: note: float > >>>>>>> std::pow(float, float) > >>>>>>> /usr/include/c++/4.4/cmath:362: note: long double > >>>>>>> std::pow(long double, long double) > >>>>>>> /usr/include/c++/4.4/cmath:369: note: double > >>>>>>> std::pow(double, int) > >>>>>>> /usr/include/c++/4.4/cmath:373: note: float > >>>>>>> std::pow(float, int) > >>>>>>> /usr/include/c++/4.4/cmath:377: note: long double > >>>>>>> std::pow(long double, int) > >>>>>>> [...] > >>>>>>> > >>>>>>> boost::math::legendre seems to rely on std::pow which is not > >>>>>>> templated, only implemented with the most common types. > >>>>>>> > >>>>>> > >>>>>> Looks like some tweaks are required to work with GMP: > >>>>>> > >>>>>> http://www.boost.org/doc/libs/1_43_0/libs/math/doc/sf_and_dist/html/math_toolkit/using_udt/use_mpfr.html > >>>>> > >>>>> That's not a bad solution, but it requires changing the > >>>>> multi-precision type from mpf (provided by GMP) to mpfr (which is a > >>>>> library that extends the floating point functionality in GMP). For > >>>>> floating-point arithmetic MPFR is much better than pure GMP. I think > >>>>> CGAL depends on MPFR, so it wouldn't even introduce new dependencies. > >>>>> The problem is that MPFR doesn't ship with a C++-wrapper (as opposed > >>>>> to GMP). Although several independent wrappers exists, none of them > >>>>> are avalilable in Debian/Ubuntu through apt. The one Boost requires is > >>>>> not updated since 2008 (MPFR has gone from version 2.3 to 3.0.1 since > >>>>> then). > >>>>> > >>>> > >>>> I've just plonked a copy of gmpfrxx in the DOLFIN dirs to test - it's > >>>> licensed under GPL. > >>> > >>> That won't work. We need LGPL. > >>> > >> > >> I meant LPGL. > > > > Good. Does it have the "or any later version"? Otherwise it's still a > > problem. > > > > No. It's LGPL 2.1. Why is that a problem?
As far as I understand it would force DOLFIN to be LGPL 2.1 only (but I hope I'm wrong). We just went through a big trouble to secure license agreements from everyone and it would not be good to restrict those agreements to a specific version. Furthermore, the agreements say v3 or later so no one has agreed to 2.1. -- Anders > Garth > > >> Garth > >> > >>>>> (Another option would be to take the same approach as Boost ourself: > >>>>> Implement the few functions that are required (pow() plus possibly a > >>>>> few more) and place it in the global namespace before including > >>>>> boost::mat::legendre), but GMP does not provide pow() when the > >>>>> exponent is a floating point number, so this is not straight forward > >>>>> without switching to MPFR). > >>>>> > >>>>> So I guess the question is whether we want to switch to MPFR now, to > >>>>> get rid of the few lines of code in Legendre.cpp (which performs > >>>>> reasonably well), when the code is likely to be thrown out pretty soon > >>>>> anyway. I vote for "no", but I have no problems with moving the entire > >>>>> ODE solvers to a separate project, then adding it back (without > >>>>> supporting extended precision) later in the form of code generation > >>>>> for time dependent problems. > >>>>> > >>>> > >>>> There are a few issues here - even if the ODE code is moved out, I think > >>>> that we should retain the polynomial and quadrature code in DOLFIN. > >>>> > >>>> Garth > >>>> > >>>>> Benjamin > >>>>> > >>>>>> > >>>>>> Garth > >>>>>> > >>>>>> > >>>>>>> Benjamin > >>>>>>> > >>>>>>>>>>>> > >>>>>>>>>>> > >>>>>>>>>>> _______________________________________________ > >>>>>>>>>>> Mailing list: https://launchpad.net/~dolfin > >>>>>>>>>>> Post to : dolfin@lists.launchpad.net > >>>>>>>>>>> Unsubscribe : https://launchpad.net/~dolfin > >>>>>>>>>>> More help : https://help.launchpad.net/ListHelp > >>>>>>>> > >>>>>>>> _______________________________________________ > >>>>>>>> Mailing list: https://launchpad.net/~dolfin > >>>>>>>> Post to : dolfin@lists.launchpad.net > >>>>>>>> Unsubscribe : https://launchpad.net/~dolfin > >>>>>>>> More help : https://help.launchpad.net/ListHelp > >>>>>>>> > >>>>>> > >>>>>> > >>>> > >> > _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
