anchor.diff:      implicit none
       integer::i
       real(kind = x_precision)                               :: temp
  -    real(kind = x_precision), parameter                    :: t_min = 0.0d0
  -    real(kind = x_precision), parameter                    :: t_max = 10.0d0
  -    integer,                  parameter                    :: nb_it = 10
  +    real(kind = x_precision), parameter                    :: t_min = 1.0d7
  +    real(kind = x_precision), parameter                    :: t_max = 1.0d10
  +    integer,                  parameter                    :: nb_it = 3
       real(kind = x_precision)                               :: sigma = 0.0d0
  -    real(kind = x_precision)                               :: Smin=0.0d0
  -    real(kind = x_precision)                               :: Smax=10.0d0
  -    real(kind = x_precision)                               :: eps=1.0d0
  +    real(kind = x_precision)                               :: Smin = 1.0d7
  +    real(kind = x_precision)                               :: Smax = 1.0d10
  +    real(kind = x_precision)                               :: eps = 1.0d0
       real(kind = x_precision)                               :: omega = 0.0d0
       real(kind = x_precision)                               :: r = 0.0d0
       type(parameters)                                       :: param
  
positive.code: 
    select case(optical_depth)
    case(1:)
       Fz = 4 * c**2 * T**4/(27. * sqrt(3.) * (K_ff + K_e) * Sigma * Sigma_0)
    case default
       Fz = 6.22d20 * 2 / state_0%Omega_0 * state_0%rho_0 *  H * rho**2 * sqrt(T*state_0%T_0)
    end select
    Q_minus             = 2._x_precision * Fz /Sigma
    Q_plus              = 9._x_precision /4._x_precision * nu * Omega**2
    f                   = Q_plus - Q_minus
    end function f
  
  
  
negative.code:   ! eps -> Precision
    ! T-> Fixed variable
    !-------------------------------------------------------------------------
    dichotomy             = (Smin+Smax)/2.
  
    if ( f(T,Smin,omega) * f(T,Smax,omega) .gt. 0.) then
       write(*,*)'This function image does not switch its sign in this particular interval.'
    endif
  