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. Garth > -- > Anders > > >>> (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 >>>>>> >>>> >>>> >> -- Garth N. Wells Department of Engineering, University of Cambridge http://www.eng.cam.ac.uk/~gnw20/ _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
