anchor.diff:  
       real(dp),parameter :: tau_max = 20._dp
   
  +    p = p_orig
  +
       killed = .false.
   
       radial = (p%r .dot. p%v) > 0.
  
positive.code:     real(dp) :: xi
      integer :: source_id
  
      killed = .false.
  
      radial = (p%r .dot. p%v) > 0.
  
negative.code: 
    end subroutine grid_integrate_noenergy
  
    subroutine grid_escape_tau(p_orig,tmax,tau,killed)
  
      implicit none
  
      ! This should work with recent compilers but not widespread yet
      ! type(photon),value :: p
      type(photon),intent(in) :: p_orig
      type(photon) :: p
  
      real(dp),intent(in) :: tmax
      real(dp),intent(out) :: tau
      logical,intent(out) :: killed
  