[Trilinos-Users] Deterministic messaging?

[Conjeepuram Subramanian, Natarajan]

Mike,
	Maybe I don't understand this issue correctly but wouldn't
guaranteeing consistency mean floating point arithmetic is commutative? 
I wasn't aware one could guarantee that with MPI-2!

Cheers,
C.S.N

-----Original Message-----
From: trilinos-users-bounces at software.sandia.gov
[mailto:trilinos-users-bounces at software.sandia.gov] On Behalf Of Heroux,
Michael A
Sent: Wednesday, June 15, 2011 9:50 AM
To: Bartlett, Roscoe A; Willenbring, James M; John R Cary; Trilinos
Users
Subject: Re: [Trilinos-Users] Deterministic messaging?

John,

As long as you are running on the same number of MPI processes on the
same
machine, without threading (for example in Epetra), you should see
bit-wise
identical results from Trilinos.

Mike


On 6/15/11 9:30 AM, "Roscoe Bartlett" <rabartl at sandia.gov> wrote:

> John,
> 
> I thought that bit-wise reproducibility with singe thread-per-process
MPI was
> guaranteed on a homogeneous machine (and is given by the MPI
implementation of
> global reduction operations).  On a heterogeneous machine I am not
sure this
> is true but you will have to talk to the MPI implementation people
about this,
> not Trilinos developers.  As long as MPI race conditions don't exist,
I don't
> think this is a Trilinos problem.
> 
> Moving to multi-core (multiple threads, etc.) changes all of this ...
> 
> -Ross
> 
> 
>> -----Original Message-----
>> From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos-
>> users-bounces at software.sandia.gov] On Behalf Of Willenbring, James M
>> Sent: Wednesday, June 15, 2011 7:42 AM
>> To: John R Cary; Trilinos Users
>> Subject: Re: [Trilinos-Users] Deterministic messaging?
>> 
>> John,
>> 
>> We have discussed this a few times at developer meetings.  The
>> consensus has been that bit-level reproducibility is prohibitively
>> expensive.  Are you able to modify the test to have some tolerance?
>> This seems to be the most common way to avoid needing bit-level
>> reproducibility.
>> 
>> Jim
>> 
>> -----Original Message-----
>> From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos-
>> users-bounces at software.sandia.gov] On Behalf Of John R Cary
>> Sent: Wednesday, June 15, 2011 6:33 AM
>> To: Trilinos Users
>> Subject: [Trilinos-Users] Deterministic messaging?
>> 
>> We have a regression test that uses a trilinos solver.
>> It seems to drift a bit (numerical errors) when run in
>> parallel but not serial.
>> 
>> Is the messaging when using trilinos solvers deterministic
>> so that one can have bit-level reproducibility?
>> 
>> Can it be made so?
>> 
>> Thx....John
>> 
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