# 1 "<stdin>"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "<stdin>"
module unbox
! helixfilter aa = cube(a1,a2,...)
  use helix
  use cartesian
  implicit none
  contains
  function unboxn( nd, center, na, cube) result( aa)
    type( filter) :: aa
    integer, dimension( :), intent( in) :: nd, center, na
    ! (ndim)
    real, dimension( :), intent( in) :: cube
    ! cube(a1,a2,...)
    logical, dimension( size( cube)) :: keep
    ! keep(a1*a2*...)
    integer, dimension( size( nd)) :: ii ! (ndim)
    integer :: ic, lag0a, lag0d, i, h
    call cart2line( na, center, lag0a)
    call cart2line( nd, center, lag0d)
    keep = ( abs( cube) > epsilon( cube))
    ! epsilon is a Fortran intrinsic
    keep( lag0a) = .false. ! throw away the 1.0.
    call allocatehelix( aa, count( keep))
    h = 0
    do ic = 1, size( cube)
! sweep cube
      if ( keep( ic) ) then
        h = h + 1 ! only the keepers
        call line2cart( na, ic, ii) ! ii(ic)= indices on na
        call cart2line( nd, ii, i) ! i = index on nd
        aa%lag( h) = i - lag0d ! lag = index - center
        aa%flt( h) = cube( ic) ! copy coefs.
      end if
    end do
  end function
end module