anchor.diff:      open(18,file = 'Temperature_Sigma.dat',status='unknown',action='readwrite') 
       write(18,*)"T Sigma"
       do i           = 1 , nb_it
  +       Smin=5.0d-4
  +       Smax=1.0d-3
          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:     real(kind=x_precision), intent(in)                     ::coeff_a,coeff_b,coeff_c
      real(kind=x_precision), intent(out)                    ::sol
      real(kind=x_precision)                                 ::delta=0.
      
      delta          = coeff_b**2 - 4 * coeff_a * coeff_c
      if (delta .lt. 0.) then
        write(*,*)'No solutions in the R field.'
  
negative.code:   else
       optical_depth     = 0
    end if
  write(*,*)'tau',tau_eff
    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)
  