anchor.diff:    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
   
  
positive.code:   return
  end subroutine compute_visc
  
  subroutine ext_forces
    use forces
    use constants
  
negative.code:           * (rho(i)+rho(nb)-2.0_WP*PARTICLE_DENSITY) &
            * q / m
  
        sx = sx + (k+scorr)*dx
        sy = sy + (k+scorr)*dy
        sz = sz + (k+scorr)*dz
  