anchor.diff:    
     !> momentum and pressure preconditioning matrix setup/factor
     function pbcPSet(c_x,c_xScale,c_f,c_fScale,dat)
  +    use iso_c_binding
  +    use modSUNDIALS
  +    use modAdvection
  +    use modPressure
       type(C_PTR),value::c_x,c_xScale,c_f,c_fScale,dat
       integer(C_INT)::pbcPSet
       double precision,pointer::x(:),xScale(:),f(:),fScale(:)
  
positive.code:     call associateVector(c_fScale,fScale)
      
      ! construct preconditioning matrix
      ! factor preconditioning matrix
      pbcPSet=0
      foo=dat
    end function
  
negative.code:   double precision,allocatable::presF(:,:) !< pressure force applied on cell [N]
    double precision,allocatable::condQ(:) !< heat conduction into cell [W]
    double precision,allocatable::H(:) !< mass-specific enthalpy [J/kg]
    
    double precision,allocatable::massFlowSensP(:,:) !< sensitivity of mass flow rate on pressure
    double precision,allocatable::pbcDiagPrec(:) !< diagonal preconditioner
    
    ! scales and scaling factors
    double precision,allocatable::rhoScale !< density scale [kg/m^3]
  