Re: [Help-gsl] ode version and compilers

[Tuomo Keskitalo]

Hi,

Thanks for the code example, I'll try to have a look at it this week.

On 11/05/2013 03:46 PM, Rhys Ulerich wrote:
> Tuomo,
> 
> Alan and Gideon have experienced some significant slowdowns in ODE
> integration going from 1.15 to 1.16.  Alan's tracked down the problem
> to a single revision...
> 
>> For the source code I have attached, I have done some tests on different
>> versions.
>> 1.15:
>> Running time: 0m0.759s
>> Output result: -0.378978 (center of mass of dynamical variables)
>>
>> 1.16
>> Running time: 0m10.670s
>> Output result: -0.378996
>>
>> 1.16 (without revision 4771):
>> Running time: 0m0.754s
>> Output result: -0.378978
>>
>> In revision 4771, the programmer intended to use e->dydt_out to update
>> e->dydt_in, rather than calculating a new e->dydt_in.  Based on my
>> understanding on the source code, he thought that memcpy is better than a
>> new calculation.  But, in my case, it makes a big performance regression.
>> Also, in my experiment, without 4771, results by 1.15 and 1.16 agree with
>> each other.  So, I would like to question which version is not reliable.
>> For the reliability concern, I have sent an email to bug-gsl to question
>> about this.
>>
>> ==============================
>>
>> The source code:
>> http://www.filedropper.com/cannstdsubdelay
> 
> Any thoughts? 
> http://bzr.savannah.gnu.org/lh/gsl/trunk/revision/4771#ode-initval2/evolve.c
> seems incredibly benign at a glance.
> 
> - Rhys
> .
> 


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