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pi_gather.f90
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Wed, Sep 11, 03:09
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Fri, Sep 13, 03:09 (2 d)
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Attached To
rSCINTROPAR Introduction to parallelism
pi_gather.f90
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! ==========================================================================
! This exercise is taken from the class Parallel Programming Workshop (MPI,
! OpenMP and Advanced Topics) at HLRS given by Rolf Rabenseifner
! ==========================================================================
program
pi_reduction
use
mpi
implicit none
integer
,
parameter
::
n
=
10000000
double precision
::
omp_t1
,
omp_t2
double precision
::
dx
,
x
,
sm
,
pif
double precision
,
external
::
f
double precision
,
allocatable
,
dimension
(:)
::
sms
integer
::
i
integer
::
ierror
,
prank
,
psize
integer
::
nlocal
,
istart
,
iend
call
MPI_init
(
ierror
)
call
MPI_Comm_size
(
MPI_COMM_WORLD
,
psize
,
ierror
)
call
MPI_Comm_rank
(
MPI_COMM_WORLD
,
prank
,
ierror
)
! calculate pi = integral [0..1] 4 / (1 + x**2) dx
omp_t1
=
MPI_Wtime
()
nlocal
=
n
/
psize
istart
=
1
+
nlocal
*
prank
iend
=
nlocal
*
(
prank
+
1
);
dx
=
1.
/
n
sm
=
0.0
;
do
i
=
istart
,
iend
x
=
(
1.
*
i
-
0.5
)
*
dx
sm
=
sm
+
f
(
x
)
enddo
allocate
(
sms
(
psize
))
if
(
prank
.eq.
0
)
then
call
MPI_Gather
(
sm
,
1
,
MPI_DOUBLE
,
sms
,
1
,
MPI_DOUBLE
,
0
,
MPI_COMM_WORLD
,
ierror
)
sm
=
0.
do
i
=
1
,
psize
sm
=
sm
+
sms
(
i
)
enddo
else
call
MPI_Gather
(
sm
,
1
,
MPI_DOUBLE
,
sms
,
0
,
MPI_DOUBLE
,
0
,
MPI_COMM_WORLD
,
ierror
);
endif
call
MPI_Bcast
(
sm
,
1
,
MPI_DOUBLE
,
0
,
MPI_COMM_WORLD
,
ierror
);
pif
=
dx
*
sm
omp_t2
=
MPI_Wtime
()
if
(
prank
.eq.
0
)
then
print
*
,
'computed pi ='
,
pif
print
*
,
'Running time = '
,
(
omp_t2
-
omp_t1
)
endif
deallocate
(
sms
)
call
MPI_Finalize
(
ierror
)
end program
pi_reduction
double precision
function
f
(
a
)
implicit none
double precision
,
intent
(
in
)
::
a
f
=
4.
/
(
1.
+
(
a
**
2
))
end function
f
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