I have found that the fortran version mpi_reduce does not work for real*18. This can be shown by the following program. I have not test the C version of mpi_reduce. c-----------------------Fortran code begins ----------------------------- implicit real*8 (a-h, o-z) include 'mpif.h' real*16 h1, h call mpi_init(ierr) call mpi_comm_size(mpi_comm_world, nprocs, ierr) call mpi_comm_rank(mpi_comm_world, myrank, ierr) h1 = (myrank+4) *2.00000000000000 write(*,'(''before reduce --'', i4,2f12.8)')myrank, h1,h call mpi_reduce(h1,h,1,mpi_long_double,mpi_sum,0, & mpi_comm_world,ierr) write(*,'(''after reduce --'',i4,2f12.8)')myrank, h1,h call mpi_bcast(h,1,mpi_long_double,0, & mpi_comm_world,ierr) write(*,'(''bcastvalue -- '',i4,2f12.8)')myrank, h1,h call mpi_finalize(ierr) end c-----------------------Fortran code begins ----------------------------- $ mpif77 a.f -o a.out $ mpirun -np 3 ./a.out before reduce -- 1 10.00000000 0.00000000 after reduce -- 1 10.00000000 0.00000000 before reduce -- 2 12.00000000 0.00000000 before reduce -- 0 8.00000000 0.00000000 after reduce -- 2 12.00000000 0.00000000 after reduce -- 0 8.00000000 8.00000000 bcastvalue -- 0 8.00000000 8.00000000 bcastvalue -- 1 10.00000000 8.00000000 bcastvalue -- 2 12.00000000 8.00000000 _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss