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? Garth > -- > Anders > > >> 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
