[MPIWG Fortran] Data type of F08 subarray

[Junchao Zhang]

Thanks, Rolf.  And I feel there is a jump from contiguous subarray to
non-contiguous subarray.

For contiguous subarray, such as

REAL s(100)
MPI_SEND(s(2:50), 3, dtype, ...)

s only gives the start address. dtype can be anything, e.g., either a basic
type or a derived type created by MPI_Type_vector() etc.

For non-contiguous subarray, such as

REAL s(100)
MPI_SEND(s(1:100:5), 3, dtype, ...)

dtype can only be MPI_REAL. In other words, dtype is kind of redundant here
since the type map is actually specified by the subarray.


--Junchao Zhang


On Tue, May 13, 2014 at 10:20 AM, Rolf Rabenseifner <rabenseifner at hlrs.de>wrote:

> Dear Junchao,
>
> MPI-3.0 p25:7-8 describes only communication with language type
> of the buffer argument matches to the MPI datatype used
> in the datatype argument.
> Same p83:36-37.
>
> Therefore, the answer is no and the compiler cannot detect
> a mismatch beteen language buffer specification and
> MPI datatype specification.
>
> I hope my answer could help.
>
> Best regards
> Rolf
>
>
> ----- Original Message -----
> > From: "Junchao Zhang" <jczhang at mcs.anl.gov>
> > To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
> > Sent: Tuesday, May 13, 2014 5:08:30 PM
> > Subject: [MPIWG Fortran] Data type of F08 subarray
> >
> >
> >
> >
> > p626 of MPI-3.0 gives such an example
> >
> >
> > REAL s(100), r(100)
> > CALL MPI_Isend(s(1:100:5), 3, MPI_REAL, ..., rq, ierror)
> >
> > All nonblocking MPI functions behave as if the user-specified
> > elements of choice buffers are copied to a contiguous scratch buffer
> > in the MPI runtime environment. All datatype descriptions (in the
> > example above, “3, MPI_REAL”) read and store data from and to this
> > virtual contiguous scratch buffer ...
> >
> > Here, data type of s(100) match with MPI_REAL, so everything is fine.
> > But I want to know if MPI permits mismatched types, for example, can
> > s(100) be an integer array? If the answer is no, then compilers can
> > not detect this error ; if yes, then it is hard to implement that.
> > To avoid memory copying to a scratch buffer, I want to use MPI
> > datatypes. But if I have two types, one is given by the choice
> > buffer itself, the other is given by the MPI_Datatype argument, how
> > could I do that?
> >
> > Any thoughts?
> >
> > Thanks
> >
> > --Junchao Zhang
> > _______________________________________________
> > mpiwg-fortran mailing list
> > mpiwg-fortran at lists.mpi-forum.org
> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>
> --
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
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