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This example computes pi by integrating f(x) = 4/(1 + x**2)
using MPI_Spawn. It starts with one process and spawns a new world
that does the computation along with the original process. Each
newly spawned process receives the # of intervals used, calculates
the areas of its rectangles, and synchronizes for a global summation.
The original process 0 prints the result and the time it took. |
program mainprog
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
integer parenticomm, spawnicomm, mergedcomm, high
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)
call MPI_COMM_GET_PARENT(parenticomm, ierr)
if (parenticomm .eq. MPI_COMM_NULL) then
print *, "Original Process ", myid, " of ", numprocs,
+ " is alive"
call MPI_COMM_SPAWN("./compute_pi_spawn", MPI_ARGV_NULL, 3,
+ MPI_INFO_NULL, 0, MPI_COMM_WORLD, spawnicomm,
+ MPI_ERRCODES_IGNORE, ierr)
call MPI_INTERCOMM_MERGE(spawnicomm, 0, mergedcomm, ierr)
call MPI_COMM_FREE(spawnicomm, ierr)
else
print *, "Spawned Process ", myid, " of ", numprocs,
+ " is alive"
call MPI_INTERCOMM_MERGE(parenticomm, 1, mergedcomm, ierr)
call MPI_COMM_FREE(parenticomm, ierr)
endif
call MPI_COMM_RANK(mergedcomm, myid, ierr)
call MPI_COMM_SIZE(mergedcomm, numprocs, ierr)
print *, "Process ", myid, " of ", numprocs,
+ " in merged comm is alive"
sizetype = 1
sumtype = 2
if (myid .eq. 0) then
n = 100
endif
call MPI_BCAST(n, 1, MPI_INTEGER, 0, mergedcomm, 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, mergedcomm, 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_COMM_FREE(mergedcomm, ierr)
call MPI_FINALIZE(ierr)
stop
end |
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compute_pi_spawn.f
output | |
The output from running the compute_pi_spawn executable is
shown below. The application was run with -np1 and with the -spawn option. Original Process 0 of 1 is alive
Spawned Process 0 of 3 is alive
Spawned Process 2 of 3 is alive
Spawned Process 1 of 3 is alive
Process 0 of 4 in merged comm is alive
Process 2 of 4 in merged comm is alive
Process 3 of 4 in merged comm is alive
Process 1 of 4 in merged comm is alive
pi is approximately: 3.1416009869231254
Error is: 0.0000083333333323 |
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Printable version
