[petsc-users] warning query

[Gideon Simpson]

What should I make of the following warning, where I have used an MPI_Allreduce on a quantity computed on each processor.

include -I/opt/local/include -I/opt/local/include/mpich-gcc48  -I/opt/local/include   `pwd`/petsc_trapz1.c
In file included from /opt/local/lib/petsc/include/petscsys.h:1794:0,
                 from /opt/local/lib/petsc/include/petscis.h:7,
                 from /opt/local/lib/petsc/include/petscvec.h:9,
                 from /Users/gideon/code/trapz/petsc_trapz1.c:3:
/Users/gideon/code/trapz/petsc_trapz1.c: In function 'main':
/opt/local/lib/petsc/include/petsclog.h:370:57: warning: value computed is not used [-Wunused-value]
   ((petsc_allreduce_ct += PetscMPIParallelComm(comm),0) || MPI_Allreduce(sendbuf,recvbuf,count,datatype,op,comm))
                                                         ^
/Users/gideon/code/trapz/petsc_trapz1.c:110:3: note: in expansion of macro 'MPI_Allreduce'
   MPI_Allreduce(&local_trapz, &global_trapz, 1, MPI_DOUBLE, MPI_SUM, PETSC_COMM_WORLD);


-gideon

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