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