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+-- Copyright 2011 by Jannis Pohlmann and 2012 by Till Tantau
+--
+-- This file may be distributed and/or modified
+--
+-- 1. under the LaTeX Project Public License and/or
+-- 2. under the GNU Public License
+--
+-- See the file doc/generic/pgf/licenses/LICENSE for more information
+
+-- @release $Header: /cvsroot/pgf/pgf/generic/pgf/graphdrawing/lua/pgf/gd/layered/CycleRemovalGansnerKNV1993.lua,v 1.1 2012/11/27 17:24:26 tantau Exp $
+
+
+local CycleRemovalGansnerKNV1993 = {}
+
+
+-- Imports
+local declare = require("pgf.gd.interface.InterfaceToAlgorithms").declare
+local Simplifiers = require "pgf.gd.lib.Simplifiers"
+
+
+function CycleRemovalGansnerKNV1993:run ()
+ -- merge nonempty sets into supernodes
+ --
+ -- ignore self-loops
+ --
+ -- merge multiple edges into one edge each, whose weight is the sum of the
+ -- individual edge weights
+ --
+ -- ignore leaf nodes that are not part of the user-defined sets (their ranks
+ -- are trivially determined)
+ --
+ -- ensure that supernodes S_min and S_max are assigned first and last ranks
+ -- reverse in-edges of S_min
+ -- reverse out-edges of S_max
+ --
+ -- ensure the supernodes S_min and S_max are are the only nodes in these ranks
+ -- for all nodes with indegree of 0, insert temporary edge (S_min, v) with delta=0
+ -- for all nodes with outdegree of 0, insert temporary edge (v, S_max) with delta=0
+
+ -- classify edges as tree/forward, cross and back edges using a DFS traversal
+ local tree_or_forward_edges, cross_edges, back_edges = Simplifiers:classifyEdges(self.graph)
+
+ -- reverse the back edges in order to make the graph acyclic
+ for _,edge in ipairs(back_edges) do
+ edge.reversed = true
+ end
+end
+
+
+-- done
+
+return CycleRemovalGansnerKNV1993 \ No newline at end of file