module nmisinput {	               # find a mask of missing filter inputs
  use nhelicon
contains
  subroutine find_mask( known, aa) {
    logical,  intent( in)          :: known(:)
    type( nfilter)                 :: aa
    real, dimension( size (known)) :: rr, dfre
    integer                        :: stat, i
    where( known) dfre = 0.    
    elsewhere     dfre = 1.    
    call nhelicon_init( aa)
    do i = 1, size( aa%hlx)
       aa%hlx( i)%flt = 1.
    stat = nhelicon_lop( .false., .false., dfre, rr)
    where ( rr > 0.)   aa%mis = .true.	
    do i = 1, size( aa%hlx)
       aa%hlx( i)%flt = 0. 
    }
}