anchor.diff:  
     neigh_t = neigh_t  + t2-t1
     dens_t  = dens_t   + t3-t2
  -  pres_t  = pres_t   + t4-t3
  -  visc_t  = visc_t   + t5-t4
  +  force_t = force_t  + t5-t3
     ef_t    = ef_t     + t6-t5
     ps_t    = ps_t     + t7-t6
   
  
positive.code:   use precision
    implicit none
  
    real(WP) :: neigh_t, dens_t, pres_t, visc_t, ef_t, ps_t, tot_t
  
  end module timers
  
  
negative.code:   return
  end subroutine compute_density
  
  subroutine compute_forces
    use constants
    use neighbors
    use posvel
  