On 02/06/11 17:33, Benjamin Kehlet wrote: > On 2 June 2011 17:49, Garth N. Wells <gn...@cam.ac.uk> wrote: >> >> >> On 02/06/11 13:41, Anders Logg wrote: >>> Anyone using or interested in the ODE solvers should take a look >>> below. >>> >>> On Thu, Jun 02, 2011 at 02:17:17PM +0200, Benjamin Kehlet wrote: >>>> On 2 June 2011 14:02, Anders Logg <l...@simula.no> wrote: >>>>> On Thu, Jun 02, 2011 at 01:10:01PM +0200, 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. >>>>> >>>>> If it's not possible to make it work, we need to revert back. >>>> >>>> I don't know of any solution to this. This is the same problem that we >>>> discussed some months back (then related to Armadillo): Templated >>>> libraries which rely on non-templated code (often old and implemented >>>> i c), so they only support the types which these underlying libraries >>>> can handle. I think the only solution here is a change in >>>> boost::math::Legendre. >>>> >>>> Of course another solution would be to split the ODE solver from >>>> Dolfin and let it continue as a separate project, and then import code >>>> from that when we are going to look at automation/generating code for >>>> time-dependent problems. >>> >>> Yes, perhaps it's time for that. Since it is going to be removed soon >>> (and replaced by code generation), the best option might be to remove >>> it before the release of 1.0. >>> >>> Are there any objections? Is anyone using the ODE solvers? >>> >> >> No objection, I think that it's a good idea. >> >> Once the ODE solvers are out, we can re-design the arbitrary precision >> interface. > > Good. Just out of curiosity: What is the need of arbitrary precision > then?
I don't have anything in particular in mind, but it is a nice feature to have. Garth > I thought the ODE solvers were the only reason for supporting > that. > > Benjamin > >> >> Garth >> >>> (They will make a comeback later in new form.) >>> >>> -- >>> Anders >> >> _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
