dolfin team mailing list archive

[Benjamin Kehlet <benjamik@xxxxxxxxx>]

On 2 June 2011 17:49, Garth N. Wells <gnw20@xxxxxxxxx> 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.

Good. Just out of curiosity: What is the need of arbitrary precision
then? I thought the ODE solvers were the only reason for supporting
that.

Benjamin

>
> Garth
>
>> (They will make a comeback later in new form.)
>>
>> --
>> Anders
>
>