George --
Just to be clear, I was not suggesting that he split on a color of
MPI_COMM_NULL. His last snippet of code was:
-----
CALL MPI_GROUP_INCL(GROUP_WORLD, nPSObranch, MRANKS, MASTER_GROUP,ierr)
CALL MPI_COMM_CREATE_GROUP(MPI_COMM_WORLD,MASTER_GROUP,0,MASTER_COMM,iErr)
!
IF(MPI_COMM_NULL .NE. MASTER_COMM)THEN
CALL MPI_COMM_RANK(MASTER_COMM, MPImaster%rank,MPIlocal%iErr)
CALL MPI_COMM_SIZE(MASTER_COMM, MPImaster%nCPU,MPIlocal%iErr)
ELSE
MPImaster%rank = MPI_PROC_NULL
ENDIF
...
IF(MPImaster%rank.GE.0)THEN
CALL MPI_SCATTER(PP, 10, MPI_DOUBLE, PPL, 10,MPI_DOUBLE, 0, MASTER_COMM,
iErr)
ENDIF
-----
In particular, the last "IF(MPImaster%rank.GE.0)" -- he's checking to see if
the MPImaster%rank was set to MPI_PROC_NULL. I was just suggesting that he
change that to "IF(MPI_COMM_NULL .NE. MASTER_COMM)" -- i.e., he shouldn't make
any assumptions about the value of MPI_PROC_NULL, etc.
> On Aug 2, 2017, at 12:54 PM, George Bosilca <[email protected]> wrote:
>
> Diego,
>
> Setting the color to MPI_COMM_NULL is not good, as it results in some random
> value (and not the MPI_UNDEFINED that do not generate a communicator). Change
> the color to MPI_UNDEFINED and your application should work just fine (in the
> sense that all processes not in the master communicator will have the
> master_comm variable set to MPI_COMM_NULL).
>
> George.
>
>
>
> On Wed, Aug 2, 2017 at 10:15 AM, Diego Avesani <[email protected]>
> wrote:
> Dear Jeff, Dear all,
>
> thanks, I will try immediately.
>
> thanks again
>
>
>
> Diego
>
>
> On 2 August 2017 at 14:01, Jeff Squyres (jsquyres) <[email protected]> wrote:
> Just like in your original code snippet, you can
>
> If (master_comm .ne. Mpi_comm_null) then
> ...
>
> Sent from my phone. No type good.
>
> On Aug 2, 2017, at 7:17 AM, Diego Avesani <[email protected]> wrote:
>
>> Dear all, Dear Jeff,
>>
>> I am very sorry, but I do not know how to do this kind of comparison.
>>
>> this is my peace of code:
>>
>> CALL MPI_GROUP_INCL(GROUP_WORLD, nPSObranch, MRANKS, MASTER_GROUP,ierr)
>> CALL MPI_COMM_CREATE_GROUP(MPI_COMM_WORLD,MASTER_GROUP,0,MASTER_COMM,iErr)
>> !
>> IF(MPI_COMM_NULL .NE. MASTER_COMM)THEN
>> CALL MPI_COMM_RANK(MASTER_COMM, MPImaster%rank,MPIlocal%iErr)
>> CALL MPI_COMM_SIZE(MASTER_COMM, MPImaster%nCPU,MPIlocal%iErr)
>> ELSE
>> MPImaster%rank = MPI_PROC_NULL
>> ENDIF
>>
>> and then
>>
>> IF(MPImaster%rank.GE.0)THEN
>> CALL MPI_SCATTER(PP, 10, MPI_DOUBLE, PPL, 10,MPI_DOUBLE, 0, MASTER_COMM,
>> iErr)
>> ENDIF
>>
>> What I should compare?
>>
>> Thanks again
>>
>> Diego
>>
>>
>> On 1 August 2017 at 16:18, Jeff Squyres (jsquyres) <[email protected]>
>> wrote:
>> On Aug 1, 2017, at 5:56 AM, Diego Avesani <[email protected]> wrote:
>> >
>> > If I do this:
>> >
>> > CALL MPI_SCATTER(PP, npart, MPI_DOUBLE, PPL, 10,MPI_DOUBLE, 0,
>> > MASTER_COMM, iErr)
>> >
>> > I get an error. This because some CPU does not belong to MATER_COMM. The
>> > alternative should be:
>> >
>> > IF(rank.LT.0)THEN
>> > CALL MPI_SCATTER(PP, npart, MPI_DOUBLE, PPL, 10,MPI_DOUBLE, 0,
>> > MASTER_COMM, iErr)
>> > ENDIF
>>
>> MPI_PROC_NULL is a sentinel value; I don't think you can make any
>> assumptions about its value (i.e., that it's negative). In practice, it
>> probably always is, but if you want to check the rank, you should compare it
>> to MPI_PROC_NULL.
>>
>> That being said, comparing MASTER_COMM to MPI_COMM_NULL is no more expensive
>> than comparing an integer. So that might be a bit more expressive to read /
>> easier to maintain over time, and it won't cost you any performance.
>>
>> --
>> Jeff Squyres
>> [email protected]
>>
>> _______________________________________________
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>>
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>
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--
Jeff Squyres
[email protected]
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