anchor.diff:  
           ! Optical thin case
   
  -        Smin          = S_max
  -        Smax          = S_min
  +        Smin          = S_min
  +        Smax          = S_max
   
           optical_depth = 0
   
  
positive.code:   subroutine curve(nb_it, eps, t_min, t_max, dt, s_min, s_max, temperature, s)
      implicit none
  
      integer                 ,                    intent(in):: nb_it 
      real(kind = x_precision),                    intent(in):: eps  
      real(kind = x_precision),                    intent(in):: t_min 
      real(kind = x_precision),                    intent(in):: t_max 
      real(kind = x_precision),                    intent(in):: dt    
      real(kind = x_precision),                 intent(inout):: S_min  
      real(kind = x_precision),                 intent(inout):: S_max  
  
      real(kind = x_precision),dimension(n_cell),intent(out) :: temperature
      real(kind = x_precision),dimension(n_cell),intent(out) :: s
  
negative.code: 
       open(fid_4,file  = fname_4, status='unknown',action='readwrite')
       !write(fid_4)'nb_cell,temp_c_thin,sigma_c_thin,temp_c_thick,sigma_thin'
  
          do i=1, n
             write(fid_4,'(1p,E12.6,4x,1p,E12.6,4x,1p,E12.6,4x,1p,E12.6,4x,1p,E12.6)')sqrt(radius(i)),&
                        temp_c_thin(i),sigma_c_thin(i),temp_c_thick(i),sigma_c_thick(i)
          end do
  
       close(fid_4)
  
    end subroutine write_critical_points
  
  
    subroutine save_data(fid, filename, n, data_1, data_2)
      implicit none
  
      integer                                  ,intent(in):: fid
      character(len =64)                       ,intent(in):: filename
      integer                                  ,intent(in):: n
      real(kind = x_precision)                 ,intent(in):: data_1
      real(kind = x_precision)                 ,intent(in):: data_2
  
      integer                                             :: i
  
      !------------------------------------------------------------------------
  
  
      open(fid,file  = filename, status='unknown',access='direct',action='readwrite')
  
  
      do i = 1, n
        write(fid,'(1p,E12.6,4x,1p,E12.6,4x,1p,E12.6)') data_1, data_2
      end do
  
      close(fid)
  
    end subroutine save_data
  