Daniel@0: function [Gs, op, nodes] = mk_nbrs_of_digraph2(G0)
Daniel@0: % MK_NBRS_OF_DIGRAPH Make all digraphs that differ from G0 by a single edge deletion, addition or reversal
Daniel@0: % [Gs, op, nodes] = mk_nbrs_of_digraph(G0)
Daniel@0: % op{i} = 'add', 'del', or 'rev' is the operation used to create the i'th neighbor.
Daniel@0: % nodes(i,1:2) are the head and tail of the operated-on arc.
Daniel@0: 
Daniel@0: [I,J] = find(G0);
Daniel@0: G0bar = setdiag(~G0, 0); % exclude self loops in graph complement
Daniel@0: [Ibar,Jbar] = find(G0bar);
Daniel@0: nnbrs = 2*length(I) + length(Ibar);
Daniel@0: Gs = cell(1, nnbrs);
Daniel@0: op = cell(1, nnbrs);
Daniel@0: nodes = zeros(nnbrs, 2);
Daniel@0: 
Daniel@0: nbr = 1;
Daniel@0: % all single edge deletions
Daniel@0: for e=1:length(I)
Daniel@0:   i = I(e); j = J(e);
Daniel@0:   G = G0;
Daniel@0:   G(i,j) = 0;
Daniel@0:   Gs{nbr} = G;
Daniel@0:   op{nbr} = 'del';
Daniel@0:   nodes(nbr, :) = [i j];
Daniel@0:   nbr = nbr + 1;
Daniel@0: end
Daniel@0: 
Daniel@0: % all single edge reversals
Daniel@0: for e=1:length(I)
Daniel@0:   i = I(e); j = J(e);
Daniel@0:   G = G0;
Daniel@0:   G(i,j) = 0;
Daniel@0:   G(j,i) = 1;
Daniel@0:   Gs{nbr} = G;
Daniel@0:   op{nbr} = 'rev';
Daniel@0:   nodes(nbr, :) = [i j];
Daniel@0:   nbr = nbr + 1;
Daniel@0: end
Daniel@0: 
Daniel@0: [I,J] = find(~G0);
Daniel@0: % all single edge additions
Daniel@0: for e=1:length(I)
Daniel@0:   i = I(e); j = J(e);
Daniel@0:   G = G0;
Daniel@0:   if i ~= j % don't add self loops
Daniel@0:     G(i,j) = 1;
Daniel@0:     Gs{nbr} = G;
Daniel@0:     op{nbr} = 'add';
Daniel@0:     nodes(nbr, :) = [i j];
Daniel@0:     nbr = nbr + 1;
Daniel@0:   end
Daniel@0: end
Daniel@0: 
Daniel@0: assert(nnbrs == nbr-1);