[Mpi-forum] MPI_2COMPLEX etc

[Richard Treumann]

Some MPI implementations have added new, predefined datatypes that are not
in the MPI Standard.  These are the the MIN_LOC/MAX_LOC operands
MPI_2COMPLEX and MPI_2DOUBLE_COMPLEX.  There is now at least one widely
used application that depends on MPI_2COMPLEX.  That application does not
port to any MPI which lacks the non-standard MPI_2COMPLEX type.

I do not recall any discussions about MPI_2COMPLEX but they probably did
occur. Some people seem convinced MPI_2COMPLEX is part of MPI-2.0.  I
searched both 2.0 and 2.2 without finding them.

I think the ambiguity in the meaning of less_than / greater_than when
applied to complex numbers would be a good reason to consider leaving the
datatypes and the associated MIN_LOC & MAX_LOC operations out of any
standard.  The idea of returning a location in a complex number is sort of
ugly too but well enough defined to be acceptable.

My understanding, going back to MPI 1.1 days, is that MPI implementations
were to avoid inventing names with an MPI_ prefix so any name with that
prefix could be used safely by follow-on MPI Fora that were extending the
standard.

We do now have these  MPI_ names among users and people are assuming the
should be able to use them portably.  I think the Forum needs to take a
position and either add them to the standard (with a clear definition of
MPI_LOC and MAX_LOC behavior) or deprecate them.

               Dick


Dick Treumann  -  MPI Team
IBM Systems & Technology Group
Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846         Fax (845) 433-8363
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