integer :: i,j
integer, parameter :: n=10000
real :: A(n,n), B(n,n), C(n,n)

do j = 1,n
  do i = 1,n
    C(i,j) = i*j
    B(i,j) = j
!   all i rows of the jth column
  enddo
enddo

do j = 1,n
  do i = 1,n
    A(i,j) = B(i,j) + C(i,j)
!   all i rows of the jth column
  enddo
enddo

end