[petsc-users] portability question for reduce operations

[Ed Bueler]

Dear PETSc --

Now that PetscGlobalSum() and related are gone, I am exposed to
MPI_Allreduce(), which is fine.

PETSc defines some MPIU_ data types, apparently for portability.  But runs
with MPIU_INT (option 1 below) break for me on one machine; this seems to
be about the petsc configuration.  I have fixed this by using option 3
below.

What is the most portable of these three, or is there yet a more portable
way?:

option 1. full use of MPIU_ types and ops:

PetscReal     x, xloc;
PetscInt        n, nloc;
MPI_Allreduce(&xloc,&x,1,MPIU_REAL,MPIU_SUM,comm);
MPI_Allreduce(&nloc,&n,1,MPIU_INT,MPIU_SUM,comm);

option 2. use of MPIU_REAL but not MPIU_INT:

PetscReal     x, xloc;
PetscInt        n, nloc;
MPI_Allreduce(&xloc,&x,1,MPIU_REAL,MPIU_SUM,comm);
MPI_Allreduce(&nloc,&n,1,MPI_INT,MPI_SUM,comm);

option 3. only use MPI's primitive MPI_ types:

PetscReal     x, xloc;
PetscInt        n, nloc;
MPI_Allreduce(&xloc,&x,1,MPI_DOUBLE,MPI_SUM,comm);
MPI_Allreduce(&nloc,&n,1,MPI_INT,MPI_SUM,comm);

I couldn't find discussion of allreduce usage in the petsc manual.

Thanks!

Ed

PS  With option 1 on one machine I get "PETSC ERROR: Can only handle
MPIU_REAL or MPIU_COMPLEX data types" in parallel but no error in serial.
On my two other machines there is no error with option 1.  All three
machines work fine with option 3.  I have not tested option 2.

-- 
Ed Bueler
Dept of Math and Stat and Geophysical Institute
University of Alaska Fairbanks
Fairbanks, AK 99775-6660
301C Chapman and 410D Elvey
907 474-7693 and 907 474-7199  (fax 907 474-5394)
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