Bug in DigraphDisjointUnion and ViewString for mutable digraphs

[wilfwilson]

Happening in 1.0.2:

gap> D := EmptyDigraph(IsMutableDigraph, 3);
<mutable empty digraph with 3 vertices>
gap> DigraphDisjointUnion(D, CycleDigraph(3));;
gap> D;
<mutable acyclic digraph with 6 vertices, 3 edges>
gap> IsAcyclicDigraph(D);
true
gap> DigraphAllSimpleCircuits(D);
[ [ 4, 5, 6 ] ]

This is worrying for two reasons: how can a mutable digraph be storing an attribute (namely the property IsAcyclicDigraph), and how can it think that it is acyclic when it clearly isn't?

[james-d-mitchell]

Hmm excellent question

[wilfwilson]

I gets worse:

gap> List(D!.OutNeighbours, IsMutable);
[ true, true, true, false, false, false ]

These should all be mutable!

[james-d-mitchell]

Here's hoping this is a bug in DigraphDIsjointUnion and not something else :)

[wilfwilson]

Yep 🙂 Should be fine - I'll look into it shortly, just doing some experiments/'research' first (which is how I discovered this).

[wilfwilson]

Resolves in v1.0.3.