openmp Loop parallelism in OpenMP Same example in Fortran
Example
program typical_loop
use omp_lib
implicit none
integer, parameter :: N = 1000000, kd = kind( 1.d0 )
real( kind = kd ) :: sum, tbegin, wtime
integer :: i
sum = 0
tbegin = omp_get_wtime()
!$omp parallel do reduction( +: sum )
do i = 1, N
sum = sum + cos( 1.d0 * i )
end do
!$omp end parallel do
wtime = omp_get_wtime() - tbegin
print "( 'Computing ', i7, ' cosines and summing them with ', i2, &
& ' threads took ', f6.4,'s' )", N, omp_get_max_threads(), wtime
if ( sum > N ) then
print *, "we only pretend using sum"
end if
end program typical_loop
Here again we compute and accumulate 1 million cosines. We time the loop and to avoid unwanted compiler optimization-away of it, we pretend using the result.
