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c                                check for quit signal 
     if ( n .le. 0 ) goto 30 
   
 
c                                calculate the interval size 
     h = 1.0d0/n 
   
 
sum  = 0.0d0 
     do 20 i = myid+1, n, numprocs 
        x   = h * (dble(i) - 0.5d0) 
        sum = sum + f(x) 
 20  continue 
     mypi = h * sum 
   
 
c                                collect all the partial sums 
     call MPI_REDUCE(mypi,pi,1,MPI_DOUBLE_PRECISION,MPI_SUM,0, 
    $     MPI_COMM_WORLD,ierr) 
   
 
c                                node 0 prints the answer. 
     if (myid .eq. 0) then 
        write(6, 97) pi, abs(pi - PI25DT) 
 97     format('  pi is approximately: ', F18.16, 
    +          '  Error is: ', F18.16) 
     endif 
   
 
goto 10 
   
 
30  call MPI_FINALIZE(rc) 
     stop 
     end

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