anchor.diff:      real(kind = x_precision), parameter                    :: t_max = 4.49d0
   
       integer, parameter                                     :: nb_it = 100
  +    real(kind = x_precision), parameter                    :: dt    = (t_max-t_min) / (nb_it-1)
   
       real(kind = x_precision)                               :: eps   = 1.0d-4
       real(kind = x_precision)                               :: eps2   = 5.0d-1
  
positive.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        = (t_max-t_min)/(nb_it-1)*(i-1) + t_min
            optical_depth = 1
  
            sigma       = dichotomy(Smin, Smax, eps, temp, omega, optical_depth)
  
negative.code:           !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
  
  