Figure 10: nominal ancestor screen
The number of ancestors of a configuration can be calculated with the help of matrices derived from the de Bruijn diagram. The row and column indices of these matrices are the partial neighborhoods of the automaton; therefore their dimension depends on the number of states and size of the neighborhood. for this reason, an LCAU program only contains the ancestor option when this combination is sufficiently small.
Unless a configuration is infinite, evolution always reduces its size; the
missing information is provided by the indices of the de Bruijn matrix. Thus
the row index describes the slightly larger left margin of the ancestral
configuration, the column index describes the right margin. Periodic
configurations depend only on the diagonal elements, those with quiescent
support depend only on the 
element, q being the quiescent state.