anchor.diff:      ! eps -> Precision
       ! T-> Fixed variable
       !-------------------------------------------------------------------------
  -    dichotomy             = (Smin+Smax)/2.
  +    S_center             = (Smin+Smax)/2.
       j = 0
       call variables(T, Smin, Omega, H, rho, cs, nu, Q_plus, Q_minus, K_ff, K_e,&
            tau_eff, P_rad, P_gaz,E_ff,Fz,f_min,Sigma_0, Omega_0,rs,T_0,rho_0,optical_depth)
  
positive.code:     write(*,"(' rs          =',1p,E12.4)") rs
      write(*,*)'****************************************'
  
      read(*,*)
  
    end subroutine display_initial_variables
  
  
negative.code: 
      if ( f_max * f_min .gt. 0.) then
     !    write(*,*)'This function image does not switch its sign in this particular interval.'
       !  dichotomy = 0
  
      else if( f_max * f_min .lt. 0.) then
         iteration:do while ( dabs( Smax - Smin ) .ge. eps .and. j .lt. 10000)
  