anchor.diff:  
          do i          = 1, nb_it
   
  -          Smin        = 1d-2
  -          Smax        = 1d54
  +          Smin        = 1d2
  +          Smax        = 1d4
   
             temp        = (t_max-t_min)/(nb_it-1)*(i-1) + t_min
             optical_depth = 1
  
positive.code: 
  ! _____________________________________________________________________________________________
  
    ! BE SURE TO CREATE TWO FILES IN YOUR WORKING DIRECTORY : s_curves ( & critical_points )        
  
    !PROBLEMATIC FOR THE SECOND CRITICAL POINT. 
  
  !_____________________________________________________________________________________________
  
  contains
    !-------------------------------------------------------------------------
    ! SUBROUTINES :
    !               curve                 : : fake main 
    !                                         --> output : 2 arrays for the coordinates (Temperature, S ) of the first critical point
    
    !               first_critical_point  : : 
    !                                     <-- input : T and Sigma for the optically thick medium + number of points
    !                                         --> output : (Temperature, Sigma) of the first critical point + index of the point
  
    !               second_critical_point  : : 
    !                                     <-- input : T and Sigma for the optically thin medium + T for the thick one + number of points + index of the thick critical point + precision
    !                                         --> output : (Temperature, Sigma) of the second critical point + index of the point
  
    !                build_s_curve         : : combining both thin and thick media 
    !                                     <-- input : T and Sigma for both media + index of the thin critical point 
    !                                         --> output : array for (Temperature, Sigma)
  
    !               quadratic              : : For a positive real solution of a quadratic equation ax^2 + bx + c =0 
    !                                     <-- input : factors a, b, c
    !                                         --> output : positive solution
   
    !               intial_variables       : : Computing some variables 
    !                                         --> output : rs, rmin, Mdot_0, Sigma_0, Omega_0, T_0 (+ nu_0 )
  
    !               variables              : : Computing all the variables for Q+ and Q-  
    !                                     <-- input : Temperature, Sigma, Omega + optical depth indicator (0 or 1) + more
    !                                         --> output : ...
  
  
    !               dichotomy              : : In order to find the result of the equation Q+ - Q- = 0
    !                                     <-- input : Temperature, Sigma, Omega + optical depth indicator (0 or 1) + precision + more
    !                                         --> output : Sigma between a computed range of surface density [Smin, Smax] for a given temperature
  
  
negative.code:     real(kind = x_precision)                               :: sigma_c_thin
      real(kind = x_precision)                               :: temp_c_thin
     ! real(kind = x_precision),dimension(n_cell)             :: sigma_thin
     ! real(kind = x_precision),dimension(n_cell)             :: temp_thin
  
      !------------------------------------------------------------------------
  
      call initial_variables(rs, rmin, Mdot_0, Sigma_0, Omega_0, T_0, rho_0)
      call display_initial_variables(rs, rmin, Mdot_0, Sigma_0, Omega_0, T_0, rho_0)
      !-------------------------------------------------------------------------
  