[Ecm-discuss] GMP-ECM finds input N

James Wanless james at grok.ltd.uk
Lun 30 Mar 17:24:19 CEST 2009


Cool! You mean you have "residue verboseness" already in GMP-ECM??! I  
might have guessed that would be the case, though I missed it when I  
looked at the --help options originally...
J

On 30 Mar 2009, at 16:14, Alexander.Kruppa at loria.fr wrote:

> Paul Zimmermann wrote:
>>        Dear Sam,
>>
>>> Date: Mon, 30 Mar 2009 08:31:32 -0400 (EDT)
>>> From: Samuel S Wagstaff <ssw at cerias.purdue.edu>
>>>
>>> Paul,
>>>
>>> Sometimes the GMP-ECM program finds the input number N, but it is
>>> printed incorrectly.  Some examples follow.  Some days it does this
>>> for 10% of the runs; other days it never does it.
>>>
>>> Have you any idea what is wrong?  I suspect a hardware or system
>>> problem, but I don't know what to tell the systems people.
>>>
>>> Thanks,
>>>
>>> Sam
>>> [...]
>> I suspect a defect memory. I have started identical runs on a Core  
>> 2 (with the
>> same version of GMP-ECM and GMP) and they do not stop immediately  
>> like yours
>> runs. To convince the systems people you could redo those runs  
>> with the same
>> parameters (e.g., echo 278...531 | ecm -sigma 4289042661  
>> 250000000). If sigma
>> is given, GMP-ECM should be deterministic. If you can produce two  
>> runs that
>> give different results, clearly it is a systems problem.
>>
>> Do other users of the computers also report similar problems?
>>
>> Hope this helps,
>> Paul
>
> You could also do runs with "residue verboseness," enabled by  
> adding "-v
> -v" to the command line. That way GMP-ECM prints the residue after  
> stage
> 1, and the product of the polynomials values at the end of stage 2. If
> these differ from one run to another with the same N, B1, B2, and  
> sigma
> values, then there's very likely something wrong with the hardware. If
> you wish to compare residues between different machines, check that  
> all
> the stage 2 parameters agree. They are printed with at least one "- 
> v", e.g.,
>
>   Using B1=50000, B2=12746592, polynomial x^2, sigma=3108370201
>   dF=512, k=5, d=4620, d2=13, i0=-2
>
>
> What type of hardware is the system that shows this erratic behaviour?
> Are the errors more likely when it is hot in the room?
>
> Best regards,
> Alex
>
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