anchor.diff:  module filters
  +
  +  ! This module defines the prototype of a filter test used by the
  +  ! Filter DFO IR Algorithm.
  +  !
  +  ! It also defines two filters: flat filter and slanting filter.
   
     abstract interface
        function absfilter(fx,hxnorm,alpha_,nf,ffilter,hfilter)
  
positive.code:   ! flat filter.                                             !
    !                                                          !
    ! Returns .true. if the point belongs to the filter or     !
    ! .false. otherwise.                                       !
    !                                                          !
    !----------------------------------------------------------!
  
  
negative.code:     ! LOCAL SCALARS
      integer :: i
  
      flatFilter = .false.
  
      do i = 1,nf
  