dolfin team mailing list archive

[Benjamin Kehlet <benjamik@xxxxxxxxx>]

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.
>
> --
> Anders
>
>
>> 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.

Benjamin

>> >>>
>> >>
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>
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