anchor.diff:            !do j          = 1, nb_it
             !   write(fid_2,'(1p,E12.6,4x,1p,E12.6,4x,1p,E12.6)')sigma_real_1(j),temp_real_1(j)
             !enddo
  +
  +          Smin        = 1d1
  +          Smax        = 1d4
   
             optical_depth = 0
   
  
positive.code:     real(kind = x_precision), parameter                    :: t_max = 4.49d0
  
      integer, parameter                                     :: nb_it = 100
  
      real(kind = x_precision)                               :: eps   = 1.0d-4
      real(kind = x_precision)                               :: eps2   = 5.0d-1
  
negative.code:        open(fid_2,file  = fname_2, status='unknown',action='readwrite')
         open(fid_3,file  = fname_3, status='unknown',action='readwrite')
  
         do i          = 1, nb_it
  
            Smin        = 1d1
            Smax        = 1d4
  
            temp        = dt * (i-1) + t_min
            optical_depth = 1
  
            sigma       = dichotomy(Smin, Smax, eps, temp, omega, optical_depth)
  