anchor.diff:      states_deriv%T = states%T + dtemp
       
       call compute_variables(states_deriv)
  -    !modification of compute_varaible--just enter a state now -- FIXME
   
       ! Let dT/dt = f0 and d²T/dt² = f1 so T(t+1) = T(t) + dt * f0 * (1 + dt * f1)
       
  
positive.code:          - s%Cv * s%v / s%x * dT_over_dx) / s%Cv
    end function f
  
  
    subroutine do_timestep_S (states)
    !process the temporal evolution of S
      use mod_variables
  
negative.code: contains
    ! (T(t+dt) - T(t))/dt = f(s, dt)
    function f (s, dt)
    !process the right term of \partial T* / \partial t* = (see Recapitulatif des adimensionenemts in report)
      implicit none
      
      type(state), intent(in)                    :: s
  