# File lib/graphviz/theory.rb, line 28 def incidence_matrix tail = (@graph.type == "digraph") ? -1 : 1 matrix = GraphViz::Math::Matrix.new( @graph.node_count, @graph.edge_count ) @graph.each_edge { |e| x = e.index nstart = @graph.get_node(e.node_one( false )).index nend = @graph.get_node(e.node_two( false )).index matrix[nstart+1, x+1] = 1 matrix[nend+1, x+1] = tail matrix[nend+1, x+1] = 2 if nstart == nend } return matrix end