diff options
Diffstat (limited to 'Master/texmf-dist/tex/generic/pgf/graphdrawing/lua/pgf/gd/layered/cycle_removal.lua')
-rw-r--r-- | Master/texmf-dist/tex/generic/pgf/graphdrawing/lua/pgf/gd/layered/cycle_removal.lua | 111 |
1 files changed, 57 insertions, 54 deletions
diff --git a/Master/texmf-dist/tex/generic/pgf/graphdrawing/lua/pgf/gd/layered/cycle_removal.lua b/Master/texmf-dist/tex/generic/pgf/graphdrawing/lua/pgf/gd/layered/cycle_removal.lua index 18670df14e8..63c43f5b14f 100644 --- a/Master/texmf-dist/tex/generic/pgf/graphdrawing/lua/pgf/gd/layered/cycle_removal.lua +++ b/Master/texmf-dist/tex/generic/pgf/graphdrawing/lua/pgf/gd/layered/cycle_removal.lua @@ -34,38 +34,39 @@ declare { phase = "cycle removal", phase_default = true, - summary = [[" - Selects a cycle removal algorithm that is especially - appropriate for graphs specified ``by hand''. + summary = [[" + Selects a cycle removal algorithm that is especially + appropriate for graphs specified ``by hand''. "]], - documentation = [[" - When graphs are created by humans manually, one can - make assumptions about the input graph that would otherwise not - be possible. For instance, it seems reasonable to assume that the - order in which nodes and edges are entered by the user somehow - reflects the natural flow the user has had in mind for the graph. - - In order to preserve the natural flow of the input graph, Gansner - et al.\ propose to remove cycles by performing a series of - depth-first searches starting at individual nodes in the order they - appear in the graph. This algorithm implicitly constructs a spanning - tree of the nodes reached during the searches. It thereby partitions - the edges of the graph into tree edges and non-tree edges. The - non-tree edges are further subdivided into forward edges, cross edges, - and back edges. Forward edges point from a tree nodes to one of their - descendants. Cross edges connect unrelated branches in the search tree. - Back edges connect descendants to one of their ancestors. It is not - hard to see that reversing back edges will not only introduce no new - cycles but will also make any directed graph acyclic. - Gansner et al.\ argue that this approach is more stable than others - in that fewer inappropriate edges are reversed compared to other - methods, despite the lack of a provable upper bound for the number - of reversed edges. - - See section~4.1.1 of Pohlmann's Diplom thesis for more details. - - This is the default algorithm for cycle removals. - "]] + documentation = [[" + When graphs are created by humans manually, one can + make assumptions about the input graph that would otherwise not + be possible. For instance, it seems reasonable to assume that the + order in which nodes and edges are entered by the user somehow + reflects the natural flow the user has had in mind for the graph. + + In order to preserve the natural flow of the input graph, Gansner + et al.\ propose to remove cycles by performing a series of + depth-first searches starting at individual nodes in the order they + appear in the graph. This algorithm + implicitly constructs a spanning tree of the nodes reached during + the searches. It thereby partitions the edges of the graph into + tree edges and non-tree edges. The non-tree edges are further + subdivided into forward edges, cross edges, and back edges. Forward + edges point from a tree nodes to one of their descendants. Cross + edges connect unrelated branches in + the search tree. Back edges connect descendants to one of their + ancestors. It is not hard to see that reversing back edges will not + only introduce no new cycles but will also make any directed graph + acyclic. Gansner et al.\ argue that this approach is more stable + than others in that fewer inappropriate edges are reversed compared + to other methods, despite the lack of a provable upper bound + for the number of reversed edges. + + See section 4.1.1 of Pohlmann's Diplom thesis for more details. + + This is the default algorithm for cycle removals. + "]] } --- @@ -75,12 +76,12 @@ declare { algorithm = "pgf.gd.layered.CycleRemovalEadesLS1993", phase = "cycle removal", - summary = [[" - This algorithm implements a greedy heuristic of Eades et al.\ for - cycle removal that prioritizes sources and sinks. + summary = [[" + This algorithm implements a greedy heuristic of Eades et al.\ for + cycle removal that prioritizes sources and sinks. "]], - documentation = [[" - See section~4.1.1 of Pohlmann's Diploma theses for details. + documentation = [[" + See section 4.1.1 of Pohlmann's Diploma theses for details. "]] } @@ -92,12 +93,12 @@ declare { algorithm = "pgf.gd.layered.CycleRemovalEadesLS1993", phase = "cycle removal", - summary = [[" - This algorithm implements a greedy heuristic of Eades et al.\ for - cycle removal that prioritizes sources and sinks. + summary = [[" + This algorithm implements a greedy heuristic of Eades et al.\ for + cycle removal that prioritizes sources and sinks. "]], - documentation = [[" - See section~4.1.1 of Pohlmann's Diploma theses for details. + documentation = [[" + See section 4.1.1 of Pohlmann's Diploma theses for details. "]] } @@ -108,13 +109,14 @@ declare { algorithm = "pgf.gd.layered.CycleRemovalBergerS1990a", phase = "cycle removal", - summary = [[" - This algorithm implements a greedy heuristic of Berger and Shor for - cycle removal. It is not really compared to the other heuristics and - only included for demonstration purposes. + summary = [[" + This algorithm implements a greedy heuristic of Berger and Shor for + cycle removal. It + is not really compared to the other heuristics and only included + for demonstration purposes. "]], - documentation = [[" - See section~4.1.1 of Pohlmann's Diploma theses for details. + documentation = [[" + See section 4.1.1 of Pohlmann's Diploma theses for details. "]] } @@ -125,12 +127,13 @@ declare { algorithm = "pgf.gd.layered.CycleRemovalBergerS1990b", phase = "cycle removal", - summary = [[" - This algorithm implements a randomized greedy heuristic of Berger - and Shor for cycle removal. It, too, is not really compared to - the other heuristics and only included for demonstration purposes. + summary = [[" + This algorithm implements a randomized greedy heuristic of Berger + and Shor for cycle removal. It, too, is not really compared to + the other heuristics and only included for demonstration purposes. "]], - documentation = [[" - See section~4.1.1 of Pohlmann's Diploma theses for details. + documentation = [[" + See section 4.1.1 of Pohlmann's Diploma theses for details. "]] - }
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