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This Fortran 77 example computes pi by integrating f(x) =
4/(1 + x2). Each process: Receives the number of intervals used
in the approximation Calculates the areas of its rectangles Synchronizes for a global summation
Process 0 prints the result of the calculation. |
program main
include 'mpif.h'
double precision PI25DT
parameter(PI25DT = 3.141592653589793238462643d0)
double precision mypi, pi, h, sum, x, f, a
integer n, myid, numprocs, i, ierr
C
C Function to integrate
C
f(a) = 4.d0 / (1.d0 + a*a)
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, myid, ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, numprocs, ierr)
print *, "Process ", myid, " of ", numprocs, " is alive"
sizetype = 1
sumtype = 2
if (myid .eq. 0) then
n = 100
endif
call MPI_BCAST(n, 1, MPI_INTEGER, 0, MPI_COMM_WORLD, ierr)
C
C Calculate the interval size.
C
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
C Collect all the partial sums.
C
call MPI_REDUCE(mypi, pi, 1, MPI_DOUBLE_PRECISION,
+ MPI_SUM, 0, MPI_COMM_WORLD, ierr)
C
C Process 0 prints the result.
C
if (myid .eq. 0) then
write(6, 97) pi, abs(pi - PI25DT)
97 format(' pi is approximately: ', F18.16,
+ ' Error is: ', F18.16)
endif
call MPI_FINALIZE(ierr)
stop
end |
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compute_pi
output | |
The output from running the compute_pi executable is shown
below. The application was run with -np = 10. Process 0 of 10 is alive
Process 1 of 10 is alive
Process 2 of 10 is alive
Process 3 of 10 is alive
Process 4 of 10 is alive
Process 5 of 10 is alive
Process 6 of 10 is alive
Process 7 of 10 is alive
Process 8 of 10 is alive
Process 9 of 10 is alive
pi is approximately: 3.1416009869231249
Error is: 0.0000083333333318 |
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Printable version
