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PROGRAM main
USE mpi
implicit none
integer ierr
integer n, i, master, myrank, nprocs
real (kind=8) h, s, x, cpi
call MPI_INIT(ierr)
call MPI_COMM_GET_PARENT(master, ierr)
call MPI_COMM_SIZE(master, nprocs, ierr)
call MPI_COMM_RANK(master, myrank, ierr)
call MPI_BCAST(n, 1, MPI_INTEGER, &
0, master, ierr)
h = 1 / DFLOAT(n)
s = 0.0
DO i=myrank+1,n,nprocs
x = h * (DFLOAT(i) - 0.5)
s = s + 4.0 / (1.0 + x*x)
END DO
cpi = s * h
call MPI_REDUCE(cpi, MPI_BOTTOM, 1, MPI_DOUBLE_PRECISION, &
MPI_SUM, 0, master, ierr)
call MPI_COMM_DISCONNECT(master, ierr)
call MPI_FINALIZE(ierr)
END PROGRAM main
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