Merge pull request #257 from MeikeWeiss/meike/subcomplex

Adaptation of SubcomplexByFaces to edge-coloured complexes

gap/PolygonalComplexes/modification.gd

@@ -576,6 +576,22 @@ DeclareOperation( "SplitEdgePathNC", [IsPolygonalComplex, IsVertexEdgePath and I
 #! The NC-version does not check whether the given set of <A>faces</A>
 #! actually consists only of faces in <A>complex</A>. It also does not
 #! check whether the result of <K>SubsurfaceByFaces</K> is a surface.
+#!
+#! In Chapter <Ref Chap="Chapter_EdgeColouring"/> the edge colouring of twisted 
+#! polygonal complexes will be introduced.
+#! 
+#! The hexagon from above can be coloured as follows:
+#! @BeginExampleSession
+#! gap> colEdges:=[ 1, 2, 1, 2, 1, 2, 3, 3, 3, 3, 3, 3 ];;
+#! gap> colSurface:=EdgeColouredPolygonalComplex(hex,colEdges);
+#! tame coloured surface (MMB with 7 vertices, 12 edges and 6 faces)
+#! @EndExampleSession
+#! If we compute a subcomplex of an edge-coloured complex, it will be edge-coloured again,
+#! induced by the edge-colouring of the given complex:
+#! @BeginExampleSession
+#! gap> SubsurfaceByFaces(colSurface,[1,2]);
+#! tame coloured surface (BMB with 4 vertices, 5 edges and 2 faces)
+#! @EndExampleSession
 #! 
 #! @Returns a twisted polygonal complex
 #! @Arguments complex, faces

gap/PolygonalComplexes/modification.gi

@@ -498,7 +498,8 @@ InstallOtherMethod( SubcomplexByFaces,
 InstallMethod( SubcomplexByFacesNC, "for a polygonal complex and a set of faces",
     [IsPolygonalComplex, IsSet],
     function(complex, subfaces)
-	local subVertices, subEdges, newVerticesOfEdges, newEdgesOfFaces, e, f;
+	local subVertices, subEdges, newVerticesOfEdges, newEdgesOfFaces, e, f,
+	    subcomplex, colEdges, colEdgesSub, edge;
 
 
         subEdges := __SIMPLICIAL_UnionSets( EdgesOfFaces(complex){subfaces} );
@@ -514,16 +515,26 @@ InstallMethod( SubcomplexByFacesNC, "for a polygonal complex and a set of faces"
 	    newEdgesOfFaces[f] := EdgesOfFaces(complex)[f];
 	od;
 
-	return PolygonalComplexByDownwardIncidenceNC( subVertices, subEdges,
+	subcomplex:=PolygonalComplexByDownwardIncidenceNC( subVertices, subEdges,
 			subfaces, newVerticesOfEdges, newEdgesOfFaces );
+	if IsEdgeColouredPolygonalComplex(complex) then
+		colEdges:=ColoursOfEdges(complex);
+        	colEdgesSub:=[];
+        	for edge in Edges(subcomplex) do
+                	colEdgesSub[edge]:=colEdges[edge];
+        	od;
+        	subcomplex:=EdgeColouredPolygonalComplexNC(subcomplex,colEdgesSub);
+	fi;
+
+	return subcomplex;
     end
 );
 InstallMethod( SubcomplexByFacesNC, 
     "for a twisted polygonal complex and a set of faces",
     [IsTwistedPolygonalComplex, IsSet],
     function(complex, subfaces)
         local remChambers, vofC, eofC, fofC, c, zeroClass, oneClass,
-            twoClass, cl;
+            twoClass, cl, subcomplex, colEdges, colEdgesSub, edge;
 
         remChambers := Union( ChambersOfFaces(complex){subfaces} );
         vofC := [];
@@ -541,7 +552,16 @@ InstallMethod( SubcomplexByFacesNC,
         twoClass := Set(twoClass);
         twoClass := Difference(twoClass, [[]]);
 
-        return TwistedPolygonalComplexByChamberRelationsNC( vofC, eofC, fofC, zeroClass, oneClass, twoClass );
+        subcomplex:=TwistedPolygonalComplexByChamberRelationsNC( vofC, eofC, fofC, zeroClass, oneClass, twoClass );
+	if IsEdgeColouredTwistedPolygonalComplex(complex) then
+        	colEdges:=ColoursOfEdges(complex);
+                colEdgesSub:=[];
+                for edge in Edges(subcomplex) do
+                	colEdgesSub[edge]:=colEdges[edge];
+                od;
+                subcomplex:=EdgeColouredTwistedPolygonalComplexNC(subcomplex,colEdgesSub);
+        fi;
+	return subcomplex;
     end
 );
 InstallOtherMethod( SubcomplexByFacesNC,