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