anchor.diff:      real(dp) :: POINT1(3),POINT2(3),POINT3(3)
       !     Local variables
       real(dp) :: ERR1(3),ERR2(3),LU,LV,U(3),V(3)
  +    real(dp),parameter :: zero_tol = 1.0e-14_dp
       logical :: check_colinear_points
       
       
  
positive.code:     
      N_U = unit_vector(U)
      N_V = unit_vector(V)
      ANGLE = scalar_product_3(N_U,N_V)
      ANGLE = max(-1.0_dp,ANGLE)
      ANGLE = min(1.0_dp,ANGLE)
      ANGLE = cos(ANGLE)
      
      angle_btwn_vectors=ANGLE
      
  
negative.code: 
  !!! list of functions
  
    ! angle_btwn_points
    ! .... returns the angle between three points
   
    ! angle_btwn_vectors
    ! .... returns the angle between two vectors
   
  