dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 03/06/11 09:11, Anders Logg wrote:
> On Fri, Jun 03, 2011 at 08:58:50AM +0100, Garth N. Wells wrote:
>>
>>
>> On 02/06/11 18:05, Anders Logg wrote:
>>> On Thu, Jun 02, 2011 at 04:49:23PM +0100, Garth N. Wells 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 <logg@xxxxxxxxx> wrote:
>>>>>>> On Thu, Jun 02, 2011 at 01:10:01PM +0200, Benjamin Kehlet wrote:
>>>>>>>> On 2 June 2011 11:51, Anders Logg <logg@xxxxxxxxx> 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.
>>>
>>> Is there a need for high precision other than for the ODE solvers?
>>> There might be a need but I don't think it's being used anywhere
>>> except for in the ODE solvers.
>>>
>>
>> Have we reached the conclusion of removing the ODE solvers from
>> lp:dolfin (for now)?
> 
> Yes.
> 

Removed.

Garth

> --
> Anders