On 02/06/11 15:21, Benjamin Kehlet wrote: > On 2 June 2011 14:59, Garth N. Wells <[email protected]> wrote: >> >> >> On 02/06/11 12:10, Benjamin Kehlet wrote: >>> On 2 June 2011 11:51, Anders Logg <[email protected]> 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. >>>> >>>> -- >>>> Anders >>>> >>>> >>>>> 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. > (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 : [email protected] >>>>>>> Unsubscribe : https://launchpad.net/~dolfin >>>>>>> More help : https://help.launchpad.net/ListHelp >>>> >>>> _______________________________________________ >>>> Mailing list: https://launchpad.net/~dolfin >>>> Post to : [email protected] >>>> Unsubscribe : https://launchpad.net/~dolfin >>>> More help : https://help.launchpad.net/ListHelp >>>> >> >> _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
