!gfortran -fopenmp -O3 timings.f90

program timings1

    use omp_lib

    implicit none
    integer, parameter :: ntests = 20
    integer :: n, nthreads
    real(kind=8), allocatable, dimension(:,:) :: a,b,c
    real(kind=8) :: t1, t2, elapsed_time
    integer(kind=8) :: tclock1, tclock2, clock_rate
    integer :: i,j,k,itest

    ! Specify number of threads to use:
    !!$ print *, "Using OpenMP, how many threads? "
    !!$ read *, nthreads
    !!nthreads=8
    !!$ call omp_set_num_threads(nthreads)
    !omp_get_num_threads()
    n=1200
    !print *, "Will multiply n by n matrices, input n: "
    !read *, n

    allocate(a(n,n), b(n,n), c(n,n))

    ! fill a and b with 1's just for demo purposes:
    a = 1.d0
    b = 1.d0

    call system_clock(tclock1)  ! start wall timer

    call cpu_time(t1)   ! start cpu timer
    do itest=1,ntests
        !$omp parallel do private(i,k)
        do j = 1,n
            do i = 1,n
                c(i,j) = 0.d0
                do k=1,n
                    c(i,j) = c(i,j) + a(i,k)*b(k,j)
                    enddo
                enddo
            enddo
        enddo

    call cpu_time(t2)   ! end cpu timer
    print 10, ntests, t2-t1
 10 format("Performed ",i4, " matrix multiplies: CPU time = ",f12.8, " seconds")

    
    call system_clock(tclock2, clock_rate)
    elapsed_time = float(tclock2 - tclock1) / float(clock_rate)
    print 11, elapsed_time
 11 format("Elapsed time = ",f12.8, " seconds")

end program timings1