anchor.diff:  
   
     !-------------------------------------------------------------------------
  -  ! secante method  in order to determine the change of sign in a given
  +  ! Secant method in order to determine the change of sign in a given
     ! interval [Smin,Smax] with an epsilon precision
     !-------------------------------------------------------------------------
  -  real(x_precision) function secante(k, i, optical_depth)
  -    implicit none
  -
  -    integer, intent(in) :: k ! Position in the disk, to get r/Omega
  -    integer, intent(in) :: i ! Iteration counter, to get the temperature
  -    integer, intent(in) :: optical_depth
  +  real(x_precision) function secant(k, i, optical_depth)
  +    implicit none
  +
  +    integer, intent(in) :: k ! Position in the disk (r/Omega)
  +    integer, intent(in) :: i ! Iteration counter (Temperature)
  +    integer, intent(in) :: optical_depth ! Indicator for the optical thickness
       !-------------------------------------------------------------------------
  -    integer           :: j
  -    real(x_precision) :: T ! Temperature used for the secante
  -    real(x_precision) :: tau_eff
  -    real(x_precision) :: Smin     ! Lowest point
  -    real(x_precision) :: Smax     ! Highest point
  -    real(x_precision) :: f_min    ! Q+ − Q− at the lowest point
  -    real(x_precision) :: f_max    ! Q+ − Q− at the highest point
  +    integer             :: j
  +    real(x_precision)   :: T ! Temperature used for the secant method
  +    real(x_precision)   :: tau_eff
  +    real(x_precision)   :: Smin     ! Lowest point
  +    real(x_precision)   :: Smax     ! Highest point
  +    real(x_precision)   :: f_min    ! Q+ − Q− at the lowest point
  +    real(x_precision)   :: f_max    ! Q+ − Q− at the highest point
       !-------------------------------------------------------------------------
   
       T = temperature(i)
  
positive.code: 
     case default
  
        write(*,*)"Optical depth is not 0 or 1"
        Fz = 0
  
      end select
  
  
negative.code: 
          ! S found with the dichotomy approach
          sigma_t_thick(i) = dichotomy(k, i, optical_depth)
          ! sigma_t_thick(i) = secant(k, i, optical_depth)
  
          ! Optical thin case (tau < 1)
          optical_depth = 0
  
          ! S found with the dichotomy approach
          sigma_t_thin(i)  = dichotomy(k, i, optical_depth)
          ! sigma_t_thin(i) = secant(k, i, optical_depth)
  
        enddo
  
        ! For the first critical point (the one at the right of the S shape)
  