!------------------------------
! dot product of two vectors
! of length 3
!------------------------------
subroutine dp(x,y,d)
  implicit none

  !-------------------------------
  ! set kind
  !-------------------------------
  integer, parameter :: rk = selected_real_kind(12)
  real(rk) :: d
  real(rk), dimension(3) :: x, y

  d = sum(x*y)

end subroutine dp