anchor.diff:      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    
  +   ! real(kind = x_precision),dimension(n_cell)             :: temp_thin
   
       !------------------------------------------------------------------------
   
  -    call display_parameters()
       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)
       !-------------------------------------------------------------------------
  
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:     if (coeff_a == 0.0) then
        write(*,*)'Coefficient a in the quadratic equation is nought.'
        continue
      else
  
  
      if (delta .lt. 0.) then
        write(*,*)'No solutions in the R field.'
  
     else
        sol_1         = -0.5_x_precision *(coeff_b + sign(sqrt(delta),coeff_b))/coeff_a
        if (sol_1 .lt. 0.d-12) then
  