[Ecm-discuss] GMP-ECM finds input N

Paul Zimmermann Paul.Zimmermann at loria.fr
Lun 30 Mar 16:24:38 CEST 2009


       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
> 
> GMP-ECM 6.1.3 [powered by GMP 4.2.2] [ECM]
> Input number is 278490841076279407188741439481565179355926725853710201632331620642982062389901741890579963524423782637435949041666525000702723914662388812510545494307250950777886431051612811386531 (180 digits)
> Using B1=250000000, B2=3178548473116, polynomial Dickson(30), sigma=4289042661
> Step 1 took 133ms
> ********** Factor found in step 1: 278490841063884187055947776611095552775304192610174976029062144974503936054006784839463424269110784886932992806801408034384896264605184267900928772020736284568064229610496951009280
> Found input number N
> 
> GMP-ECM 6.1.3 [powered by GMP 4.2.2] [ECM]
> Input number is 14934281803738074833846530939409385751024026044300465118534154673896853000327668729857703720112054704958367178027970628991322333492709062468099971107486071617412384700105582187783796209467840083368845344499411394764018753571730339338183895417675798252986998481786698140379322970784655881751945808698842016800757 (311 digits)
> Using B1=250000000, B2=3178548473116, polynomial Dickson(30), sigma=4254596094
> Step 1 took 63ms
> ********** Factor found in step 1: 14934281803738074834290000000000000000000000000000022774650429145605471433008050669126238650976000012109565521690244244583648181169689730551988407030037758222473894182000000000363419362147803445294362907042199506784028193911691292084540376000021885330143810168345823959145900109032001222492440063017207212302325
> Found input number N

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




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