anchor.diff:  
       select case(ventilation_values%expiration_type)
          
  -    case("active")
  +    case('active')
          if(ttime.lt.Tinsp)then
  -          dpmus = ventilation_values%P_muscle_estimate*ventilation_values%factor_P_muscle_insp*PI* &
  +          dP_muscle = ventilation_values%P_muscle_estimate*ventilation_values%factor_P_muscle_insp*PI* &
                  sin(pi/Tinsp*ttime)/(2.0_dp*Tinsp)*dt
          elseif(ttime.le.Tinsp+Texpn)then
  -          dpmus = ventilation_values%P_muscle_estimate*ventilation_values%factor_P_muscle_expn*PI* &
  +          dP_muscle = ventilation_values%P_muscle_estimate*ventilation_values%factor_P_muscle_expn*PI* &
                  sin(2.0_dp*pi*(0.5_dp+(ttime-Tinsp)/(2.0_dp*Texpn)))/ &
                  (2.0_dp*Texpn)*dt
          endif
          
  -    case("passive")
  +    case('passive')
          if(ttime.le.Tinsp+0.5_dp*dt)then
  -          dpmus = ventilation_values%P_muscle_estimate*ventilation_values%factor_P_muscle_insp*PI*dt* &
  +          dP_muscle = ventilation_values%P_muscle_estimate*ventilation_values%factor_P_muscle_insp*PI*dt* &
                  sin(pi*ttime/Tinsp)/(2.0_dp*Tinsp)
  -          sum_dpmus = sum_dpmus+dpmus
  -          sum_dpmus_ei = sum_dpmus
  +          sum_dP_muscle = sum_dP_muscle+dP_muscle
  +          sum_dP_muscle_ei = sum_dP_muscle
          else
             Tpass = 0.1_dp
  -          dpmus = MIN(-sum_dpmus_ei/(Tpass*Texpn)*dt,-sum_dpmus)
  -          sum_dpmus = sum_dpmus+dpmus
  +          dP_muscle = MIN(-sum_dP_muscle_ei/(Tpass*Texpn)*dt,-sum_dP_muscle)
  +          sum_dP_muscle = sum_dP_muscle+dP_muscle
          endif
          
       end select
       
  -    p_mus = p_mus + dpmus !current value for muscle pressure
  +    P_muscle = P_muscle + dP_muscle !current value for muscle pressure
   
       call enter_exit(sub_name,2)
   
  
positive.code:             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
  
negative.code: !!! the pressures throughout the tree.
  
      ! set the increment in driving (muscle) pressure
      call set_driving_pressures(dP_muscle,dt,P_muscle,Texpn,Tinsp,ttime)
      prev_flow = elem_field(ne_Vdot,1)
      
  !!! Solve for a new flow and pressure field
  