Allow specifying vertex colours in IsDigraphHomomorphism etc. #283
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flsmith
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james-d-mitchell
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Jan 23, 2020
doc/isomorph.xml
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| @@ -783,6 +785,21 @@ gap> OutNeighbours(canon); | |||
| </List> | |||
| See also <Ref Attr="AutomorphismGroup" Label="for a digraph" | |||
| />.<P/> | |||
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| If <A>col1</A> and <A>col2</A>, or <A>col</A>, are given then they must | |||
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Missing comma before "then"
doc/isomorph.xml
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| If <A>col1</A> and <A>col2</A>, or <A>col</A>, are given then they must | ||
| represent vertex colourings; see <Ref Oper="AutomorphismGroup" Label="for a | ||
| digraph and a homogeneous list"/> for details of the permissible values for | ||
| these argument. The homomorphism must then also have the property: |
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"argument" should be "arguments"
gap/grahom.gi
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| [IsDigraph, IsDigraphByOutNeighboursRep, IsTransformation, IsList, IsList], | ||
| function(src, ran, x, c1, c2) | ||
| local y, induced, i, j; | ||
| if not IsDigraphMonomorphism(src, ran, x, c1, c2) then |
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Is there some reason to not make the method for IsDigraphEmbedding analogous to the ones for IsDigraphMonomorphism? Or perhaps write a single function RespectsColouring so that all of these methods become:
function(src, ran, x, c1, c2)
return IsDigraphHomomorphism(src, ran, x) and RespectsColouring(src, ran, x);
end;
where IsDigraphHomomorphism is replaced with IsDigraphMonomorphism or IsDigraphEmbedding as appropriate?
gap/grahom.gi
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| # this global function tests whether <x> respects the colouring, i.e. whether | ||
| # for all vertices i in <src>, cols[i] = cols[i ^ x]. | ||
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| InstallGlobalFunction(DIGRAPHS_RespectsColouring, |
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Why not make this a documented operation?
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No reason, I realised that would be better a few minutes after pushing...
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doc/grahom.xml
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| The operation <C>DigraphsRespectsColouring</C> verifies whether or not | ||
| the permutation or transformation <A>x</A> respects the vertex colourings | ||
| <A>col1</A> and <A>col2</A> of the digraphs <A>src</A> and <A>range</A>. | ||
| That is, <C>DigraphsRespectsColouring</C> returns true if and only if for |
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"true" -> "<K>true</K>"
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This PR adds the ability to specify vertex colours in the operations