anchor.diff:  ! One step of SPH                       !
   ! ===================================== !
   subroutine step
  -  use posvel
  +  use constants
     use state
     use timers
     implicit none
  
positive.code:         do stz = -1, 1
            cbinz = binz + stz
            if(cbinz.lt.1 .or. cbinz.gt.nbinz) cycle
            do j = 1, max_part_guess
              if (binpart(j,cbinx,cbiny,cbinz) .eq. 0) exit
              p = binpart(j,cbinx,cbiny,cbinz)
              distx = px(i) - px(p)
              disty = py(i) - py(p)
              distz = pz(i) - pz(p)
              tdist = sqrt(distx*distx + disty*disty + distz*distz)
              if(tdist .lt. h .and. p.ne.i) then
                q = q + 1
                nbs(i,q) = binpart(j,cbinx,cbiny,cbinz)
              end if
  
negative.code:   integer , parameter :: ARTIFICIAL_PRESSURE_POWER = 4
    real(WP), parameter :: ARTIFICIAL_PRESSURE_STRENGTH = 1.0e-5_WP
    real(WP)  :: ARTIFICIAL_PRESSURE_RADIUS, PRESSURE_RADIUS_FACTOR
    logical, parameter :: USE_SURFACE_TENSION = .false.
  
  
  end module constants
  
  