anchor.diff:              lung_mechanics%b)**2.0_dp *(lambda**2.0_dp-1.0_dp)**2.0_dp/lambda**2.0_dp+(3.0_dp* &
               lung_mechanics%a+lung_mechanics%b) *(lambda**2.0_dp+1.0_dp)/lambda**4.0_dp)
          unit_field(nu_comp,nunit) = undef/unit_field(nu_comp,nunit) ! V/P
  -       ! add the chest wall (proportionately) in parallel
  -       unit_field(nu_comp,nunit) = 1.0_dp/(1.0_dp/unit_field(nu_comp,nunit)&
  -            +1.0_dp/(lung_mechanics%chest_wall_compliance/dble(num_units)))
          !estimate an elastic recoil pressure for the unit
          unit_field(nu_pe,nunit) = lung_mechanics%c/2.0_dp*(3.0_dp*lung_mechanics%a + &
               lung_mechanics%b)*(lambda**2.0_dp -1.0_dp)*exp_term/lambda
  
positive.code:           
            if(abs(ventilation_values%tidal_volume).gt.1.0e-5_dp)THEN
               ! modify driving muscle pressure by volume_target/sum_tidal
               ! this increases p_mus for volume_target>sum_tidal, and
               ! decreases p_mus for volume_target<sum_tidal
               ventilation_values%factor_P_muscle_insp = ventilation_values%factor_P_muscle_insp * &
                    abs(ventilation_values%tidal_volume/sum_tidal)
               ventilation_values%factor_P_muscle_expn = ventilation_values%factor_P_muscle_expn * &
  
negative.code: 
  !!!#############################################################################
  
    subroutine set_driving_pressures(dP_muscle,dt,P_muscle,Texpn,Tinsp,ttime)
  
      real(dp),intent(in) :: dt,Texpn, &
           Tinsp,ttime
      real(dp) :: dP_muscle,P_muscle
      ! Local variables
      real(dp) :: sum_dP_muscle,sum_dP_muscle_ei,Tpass
      character(len=60) :: sub_name
      
      ! --------------------------------------------------------------------------
  