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. 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
