module helix  
! DEFINE helix filter type
    implicit none
  type filter  
    real,    dimension( :), pointer :: flt      
    ! (nh) filter coefficients
    integer, dimension( :), pointer :: lag      ! (nh) filter lags
    logical, dimension( :), pointer :: mis      
    ! (nd) boundary conditions
  end type
  contains
  subroutine allocatehelix( aa, nh )
! allocate a filter
    type( filter) :: aa
    integer       :: nh				! count of filter coefs (excl 1)
    allocate( aa%flt( nh), aa%lag( nh))		! allocate filter and lags.
    nullify( aa%mis)				! set null pointer for "mis".
    aa%flt = 0.					! zero filter coef values
  end subroutine 
  subroutine deallocatehelix( aa)
! destroy a filter
    type( filter) :: aa
    deallocate( aa%flt, aa%lag)			! free memory
    if ( associated( aa%mis)) then
! if logicals were allocated
      deallocate( aa%mis)			! free them
    end if
  end subroutine 
end module