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 <[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. > >>>> > >>>> > >>>> > >>>>> 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. -- 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 : [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
