pi_critical_correct.f90
327098198a93master

pi_critical_correct.f90
View Options

			! ==========================================================================
			! This exercise is taken from the class Parallel Programming Workshop (MPI,
			! OpenMP and Advanced Topics) at HLRS given by Rolf Rabenseifner
			! ==========================================================================

			program pi_critical_correct

			implicit none

			integer :: myrank, num_threads
			integer, parameter :: n = 10000000
			double precision :: omp_t1, omp_t2
			double precision :: dx, x, sm, lsm, pif
			double precision, external :: second,f
			!$ double precision, external :: omp_get_wtime
			integer :: i

			! calculate pi = integral [0..1] 4 / (1 + x*2) dx /
			omp_t1 = second()
			!$ omp_t1 = omp_get_wtime()

			sm = 0.0;
			!$OMP parallel private(x,lsm) shared(sm)
			dx = 1. / n
			lsm = 0.
			!$OMP do
			do i = 1, n
			x = (1. * i - 0.5) * dx
			lsm = lsm + f(x)
			enddo
			!$OMP end do
			!$OMP critical
			sm = sm + lsm
			!$OMP end critical
			!$OMP end parallel

			pif = dx * sm

			omp_t2 = second()
			!$ omp_t2 = omp_get_wtime()

			print *, 'computed pi =',pif
			print *, 'Running time = ', (omp_t2-omp_t1)

			end program pi_critical_correct


			double precision function f(a)
			implicit none
			double precision, intent(in) :: a
			f = 4. / (1. + (a**2))
			end function f