c Program to measure time to carry out matrix-vector product.
c c(i) = sum(a(j,i)*b(j),j=1,...,n) for i=1,...,n
      program main
      implicit none
      integer i, j, k, n
      integer, allocatable :: a(:,:), b(:), c(:)
      integer*8 time0, time1, dtime
      real*8 time
c
      write(*,*)"Matrix size    Elapsed time [sec]"
      do k=1,30
c Matrix size
        n = k * 1000

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

c Initialization
        do i=1,n
          do j=1,n
            a(j,i) = 1
          end do
          b(i) = 1
        end do

c Start time
        call system_clock(time0)

c Main calculation: matrix-vector product
        do i=1,n
          c(i) = 0
          do j=1,n
            c(i) = c(i) + a(j,i) * b(j)
          end do
        end do

c Finish time
        call system_clock(time1, dtime)

c Output time
        time = 1d0*(time1-time0)/dtime
        write(*,"(i12,f16.7)")n, time

c Deallocation
        deallocate(a, b, c)
      end do

      end program