anchor.diff:      do i           = 1 , nb_it
          temp        = (t_max-t_min)/(nb_it-1)*(i-1) + t_min
          sigma       = dichotomy(Smin, Smax, eps, temp, omega)
  +       Smin=1.0e-3
  +       Smax=1.0d0
          
          write(18,*)temp," ",sigma
       enddo
  
positive.code:   end if
  
    select case(optical_depth)
    case(1:)
       Fz = 4._x_precision * c**2 * T**4/(27. * sqrt(3._x_precision) * (K_ff + K_e) * Sigma * Sigma_0)
    case default
       Fz = 6.22d20 * 2._x_precision / state_0%Omega_0 * state_0%rho_0 *  H * rho**2 * sqrt(T*state_0%T_0)
  
negative.code:      iteration:do while ( dabs( Smax - Smin ) .ge. eps .and. j .lt. N)
          if( f(T,Smin,omega) * f(T,dichotomy,omega) .lt. 0.) then
             Smax         = dichotomy
             write(*,*)'smin=',smin,' smax=', smax
          else
             Smin         = dichotomy
             write(*,*)'smin=',smin,' smax=', smax
          endif
          dichotomy       = (Smin+Smax)/2.0d0
          j               = j + 1
  