anchor.diff:           - 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
  
positive.code:     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)
      
  
negative.code: 
    subroutine do_timestep_T(states) 
    !process the temporal evolution of T
      implicit none
      
      type (state), intent(inout)                   :: states
  