Implementing DigraphEdgeConnectivity by RheyaM · Pull Request #884 · digraphs/Digraphs

RheyaM · 2025-11-21T10:19:55Z

Implemented two methods for calculating the EdgeConnectivity of a Digraph, one using Spanning Trees and one using Dominating Sets, based on the Algorithms detailed in: https://www.cse.msu.edu/~cse835/Papers/Graph_connectivity_revised.pdf

Additional functions: DigraphDominatingSet() and DigraphGetNeighbourhood(), for getting a Dominating Set of a digraph and getting the neighbourhood of a subset of vertices in a digraph, respectively.

reiniscirpons

Thanks for the implementation! I had some suggestions for the documentation and for improving the performance of the methods. Mainly more details in the docs and reworking some loops to implement more efficient DFS.

Some other things:

The documentation is not currently linked in the manual. You should edit the correct doc/z-chapX.xml file to add this. For example, to get the DigraphDominatingSet documentation to show up you should add the <#Include Label="DigraphDominatingSet"> tag in the correct place of doc/z-chap4.xml. You can test this by seeing if ?DigraphDominatingSet shows up the docs after running DigraphsMakeDoc() in gap. Same applies for the other functions.
Functions need to be more careful about symmetric vs non symmetric digraphs.
You should re-run the benchmarks after making the performance based changes to the implementation. I think currently the benchmarks are skewed by the time it takes to find the dominating set/spanning tree, but after the reimplementation this time should become negligible, and it will be more about how many vertices need to be checked. So maybe hold-off on removing the methods for now.

Afterwards should be good to merge!

mtorpey · 2026-04-23T09:37:41Z

@RheyaM, I wonder if you could merge or rebase to resolve the merge conflicts with the current main branch. Then could you indicate whether you think you've resolved @reiniscirpons's comments? We can then review this again.

…tions) added

…implemented methods

…nges for efficiency

…r symmetric digraphs

reiniscirpons · 2026-09-23T14:48:21Z

Thanks again for the PR @RheyaM ! I took some time to finish off some minor polish so we can merge into main.

@mtorpey @james-d-mitchell Could either of you give this a review when you have the time please?

codecov · 2026-09-23T15:14:16Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.46%. Comparing base (8d49e9a) to head (38b4803).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #884      +/-   ##
==========================================
+ Coverage   97.45%   97.46%   +0.01%     
==========================================
  Files          50       50              
  Lines       21189    21301     +112     
  Branches      639      639              
==========================================
+ Hits        20649    20761     +112     
  Misses        475      475              
  Partials       65       65

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Resolved

james-d-mitchell

Some superficial changes, then I'm happy to merge this

james-d-mitchell · 2026-09-24T07:07:25Z

+      <M>S</M> and repeatedly adding to <M>S</M> the least vertex that is not
+      in <M>S</M> and not and out-neighbour of <M>S</M>.
+
+      See also <Ref Oper="IsDigraphOutDominatingSet"/> for a further


Suggested change

See also <Ref Oper="IsDigraphOutDominatingSet"/> for a further

See also <Ref Oper="IsDigraphOutDominatingSet"/> for further

james-d-mitchell · 2026-09-24T07:08:56Z

+      in-dominating set</E> of <A>digraph</A> with respect to the ordering
+      <M>1 &lt; 2 &lt; ... &lt; n</M> where <M>n</M> is the number of vertices in
+      <A>digraph</A>. This is equivalently the greedy out-dominating set of
+      the <Ref Attr="DigraphDual"/> of <A>digraph</A>.


Suggested change

the <Ref Attr="DigraphDual"/> of <A>digraph</A>.

the <Ref Attr="DigraphReverse"/> of <A>digraph</A>.

The dual is the graph where every non-edge becomes an edge and vice versa, do you mean the reverse?

james-d-mitchell · 2026-09-24T07:10:04Z

+      ordering <A>order</A>) vertex that is not in <M>S</M> and not and
+      out-neighbour of <M>S</M>.
+
+      See also <Ref Oper="IsDigraphOutDominatingSet"/> for a further


Suggested change

See also <Ref Oper="IsDigraphOutDominatingSet"/> for a further

See also <Ref Oper="IsDigraphOutDominatingSet"/> for further

james-d-mitchell · 2026-09-24T07:10:21Z

+      in-dominating set</E> of <A>digraph</A> with respect to the ordering
+      that the list <A>order</A> induces on the vertices in
+      <A>digraph</A>. This is equivalently the greedy out-dominating set of
+      the <Ref Attr="DigraphDual"/> of <A>digraph</A>.


Suggested change

the <Ref Attr="DigraphDual"/> of <A>digraph</A>.

the <Ref Attr="DigraphReverse"/> of <A>digraph</A>.

Same comment as above.

james-d-mitchell · 2026-09-24T07:10:39Z

 </ManSection>
 <#/GAPDoc>

+


Suggested change

No change required in this file.

james-d-mitchell · 2026-09-24T07:11:24Z

+# vertices such that every vertex in vertices is in S or adjacent
+# to a vertex in S.
+#
+# This is done in a greedy manner by including every vertex in


This is probably not important, but can you possibly reflow this comment, the line breaks look weird to me.

james-d-mitchell · 2026-09-24T07:13:05Z

+    return 0;
+  fi;
+
+  EdgeD := UnitEdgeWeightedDigraph(DigraphImmutableCopyIfMutable(digraph));


Move this line down to just before if Length(D) > 1 then no point in doing this here, again a minor point.

james-d-mitchell · 2026-09-24T07:14:21Z

+  fi;
+
+  return Minimum(min,
+    Minimum(Minimum(OutDegrees(EdgeD)),


Minimum is associative, no? So this could just be Minimum(min, Minimum(OutDegrees(EdgeD)), Minimum(InDegrees(EdgeD)), right?

james-d-mitchell · 2026-09-24T07:15:14Z

+    if not Length(vertex_order) = DigraphNrVertices(digraph) or
+       not Set(vertex_order) = DigraphVertices(digraph) then


Suggested change

if not Length(vertex_order) = DigraphNrVertices(digraph) or

not Set(vertex_order) = DigraphVertices(digraph) then

if Length(vertex_order) <> DigraphNrVertices(digraph) or

Set(vertex_order) <> DigraphVertices(digraph) then

james-d-mitchell · 2026-09-24T07:15:29Z

+  [IsDigraph, IsList],
+  function(digraph, vertex_order)
+    if not Length(vertex_order) = DigraphNrVertices(digraph) or
+       not Set(vertex_order) = DigraphVertices(digraph) then


Same comment as above

Joseph-Edwards requested a review from reiniscirpons November 26, 2025 14:20

RheyaM force-pushed the EdgeConnectivity branch from 91c80c5 to 0634eed Compare November 26, 2025 15:07

reiniscirpons previously requested changes Dec 3, 2025

View reviewed changes

rm387 and others added 24 commits September 23, 2026 16:41

Added SwapDigraphs and DigraphsRemoveAllEdges functions

90a9a89

Fixed gaplint errors

3027792

Changes made to SwapDigraphs and DigraphRemoveAllEdges

300ebc5

Changes made to DigraphRemoveAllEdges

72e68c4

More changes made to DigraphRemoveAllEdges

e697fa4

DigraphEdgeConnectivity and additional functions (Dominating Set func…

15a5150

…tions) added

Added explanations for each Algorithm and edited gapdocs + tests for …

05f99d5

…implemented methods

Minor gaplint/test changes made

57c908e

Added DigraphEdgeConnectivityDS tests to weights.tst

60505dc

Added tests for DigraphDominatingSet()

e1bbe0c

Fixes made to Spanning Tree Algorithm + tests added to weights.tst

4205ed0

Tests added to testinstall.tst for DigraphEdgeConnectivityDS()

531fc71

Removing Spanning Tree Algorithm

75ac98a

Documentation changes + some DigraphsDominatingSet implementation cha…

c3645ab

…nges for efficiency

Removing DigraphsOutNeighbourhood

bcf23b8

Changing DigraphEdgeConnectivity and associated tests to work only fo…

dfec296

…r symmetric digraphs

Move EdgeConnectivity to attr

37a044e

Small formatting fixes etc

acc9c0d

Improve wording a little

35128b6

Factor out dominating set and add it as attr

a167c36

Finish adding tests for dominating set

94f52e1

Add more tests for EdgeConnectivity, fix mutability bug

47be251

Add docs

06e5fdf

Fix minor issue with testinstall

38b4803

reiniscirpons force-pushed the EdgeConnectivity branch from 18ef784 to 38b4803 Compare September 23, 2026 14:45

reiniscirpons requested review from james-d-mitchell, mtorpey and reiniscirpons September 23, 2026 14:50

james-d-mitchell requested changes Sep 24, 2026

View reviewed changes

	See also <Ref Oper="IsDigraphOutDominatingSet"/> for a further
	See also <Ref Oper="IsDigraphOutDominatingSet"/> for further

	the <Ref Attr="DigraphDual"/> of <A>digraph</A>.
	the <Ref Attr="DigraphReverse"/> of <A>digraph</A>.

		if not Length(vertex_order) = DigraphNrVertices(digraph) or
		not Set(vertex_order) = DigraphVertices(digraph) then

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RheyaM commented Nov 21, 2025

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reiniscirpons commented Sep 23, 2026

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codecov Bot commented Sep 23, 2026

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