subroutine tab(f,x1,x2,n,a)
      implicit none
      integer n
      double precision f, x1, x2, a(*)
      
      integer i
      real dx
      
      dx = (x2-x1)/dble(n-1)
      
      do i=1, n
        a(i) = f(x1+dble(i-1)*dx)
      end do         
      
      end