Attempt to change over to Transformation.

gap/oper.gi

@@ -797,7 +797,7 @@ InstallMethod(AmalgamDigraphs,
 "for a digraph, a digraph, a list, and a list",
 [IsDigraph, IsDigraph, IsList, IsList],
 function(D1, D2, subdigraphVertices1, subdigraphVertices2)
-  local D, map, vertex, vertexList, size, iterator, edgeList;
+  local D, map, vertex, vertexList, size, iterator, edgeList, edge;
 
   if not InducedSubdigraph(DigraphImmutableCopyIfMutable(D1),
          subdigraphVertices1) = 
@@ -810,52 +810,69 @@ function(D1, D2, subdigraphVertices1, subdigraphVertices2)
   fi;
 
   # Create a mutable copy so that the function also works on
-  # immutable input digraphs.
+  # immutable input digraphs and also does not change mutable
+  # digraphs in place.
   D := DigraphMutableCopy(D1);
 
   # 'map' is a mapping from the vertices of D2 to the vertices of the
   # final output graph. The idea is to map the subdigraph vertices of D2
   # onto the subdigraph vertices of D1 and then map the rest of the vertices
   # of D2 to other (higher) values. The mapping from D1 to the output graph
   # can be understood as the identity mapping.
-  map := rec();
+  map := [1 .. DigraphNrVertices(D2)];
 
   for vertex in [1 .. Length(subdigraphVertices1)] do
-    map.(subdigraphVertices2[vertex]) := subdigraphVertices1[vertex];
+    map[subdigraphVertices2[vertex]] := subdigraphVertices1[vertex];
   od;
 
   # Delete??
-  vertexList := Difference(DigraphVertices(D2), subdigraphVertices2);
-  size := DigraphNrVertices(D1);
+  # vertexList := Difference(DigraphVertices(D2), subdigraphVertices2);
+  # size := DigraphNrVertices(D1);
+  # iterator := 1;
+  # for vertex in vertexList do
+  #   map[vertex] := iterator + size;
+  #   iterator := iterator + 1;
+  # od;
+
+
   iterator := 1;
-  for vertex in vertexList do
-    map.(vertex) := iterator + size;
-    iterator := iterator + 1;
+  for edge in [1 .. DigraphNrEdges(D2)] do
+    Add(edgeList, []);
+    for vertex in [1, 2] do
+      if DigraphEdges(D2)[edge][vertex] in subdigraphVertices2 then
+        DigraphEdges(D2)[edge][vertex] := DigraphEdges(D2)[edge][vertex] ^ Transformation(map);
+      else
+        DigraphEdges(D2)[edge][vertex] := # But we still need a mapping for the non-subdigraph vertices
+      fi;
+    od;
   od;
 
+
+
   # The problem with adding edges to the output graph was that the
   # edges of the subdigraph were added twice, creating multiple
   # edges between certain pairs of points. A quick and readable fix
   # would have been to use DigraphRemoveAllMultipleEdges, but I decided
   # to check each of the edges being added to see if they were already
   # in the subdigraph. This way the function does not end up adding edges
   # only to delete them later.
-  edgeList := ShallowCopy(DigraphEdges(D2));
-  iterator := 1;
-  while iterator <= Length(edgeList) do
-    if edgeList[iterator][1] in subdigraphVertices2 and
-        edgeList[iterator][2] in subdigraphVertices2 then
-      Remove(edgeList, iterator);
-    else
-      edgeList[iterator] := [
-        map.(edgeList[iterator][1]), map.(edgeList[iterator][2])];
-      iterator := iterator + 1;
-    fi;
-  od;
+
+  # edgeList := ShallowCopy(DigraphEdges(D2));
+  # iterator := 1;
+  # while iterator <= Length(edgeList) do
+  #   if edgeList[iterator][1] in subdigraphVertices2 and
+  #       edgeList[iterator][2] in subdigraphVertices2 then
+  #     Remove(edgeList, iterator);
+  #   else
+  #     edgeList[iterator] := [
+  #       map.(edgeList[iterator][1]), map.(edgeList[iterator][2])];
+  #     iterator := iterator + 1;
+  #   fi;
+  # od;
 
   DigraphAddVertices(D, DigraphNrVertices(D2) - Length(subdigraphVertices1));
   DigraphAddEdges(D, edgeList);
-  return [Immutable(D), map];
+  return [Immutable(DigraphRemoveAllMultipleEdges(D)), map];
 end);
 
 ###############################################################################

tst/standard/oper.tst

@@ -2772,7 +2772,9 @@ gap> U := AmalgamDigraphs(D1, D2, [2, 3, 6, 7], [4, 5, 6, 7]);
 [ <immutable digraph with 11 vertices, 32 edges>, 
   rec( 1 := 9, 2 := 10, 3 := 11, 4 := 2, 5 := 3, 6 := 6, 7 := 7 ) ]
 gap> AmalgamDigraphs(D1, D2, [3, 6, 2, 7], [4, 5, 7, 6]);
-Error, the two subdigraphs must be equal.
+Error, the subdigraph induced by the 3rd argument (a list) in the 1st argument\
+ (a digraph) does not equal the subdigraph induced by the 4th argument (a list\
+) in the 2nd argument (a digraph)
 gap> D1 := PetersenGraph();;
 gap> U := AmalgamDigraphs(D1, D1, [3, 4, 6, 8, 9], [3, 4, 6, 8, 9]);
 [ <immutable digraph with 15 vertices, 50 edges>, 
@@ -2790,7 +2792,9 @@ gap> U := AmalgamDigraphsIsomorphic(D1, D2, [3, 4, 6, 8, 9],
   rec( 1 := 11, 2 := 3, 3 := 12, 4 := 4, 5 := 8, 6 := 9, 7 := 6, 8 := 13 ) ]
 gap> U := AmalgamDigraphsIsomorphic(D1, D2, [3, 4, 10, 8, 9],
 >   [2, 4, 5, 6, 7]);
-Error, the two subdigraphs must be isomorphic.
+Error, the subdigraph induced by the 3rd argument (a list) in the 1st argument\
+ (a digraph) is not ismorphic to the subdigraph induced by the 4th argument (a\
+ list) in the 2nd argument (a digraph)
 
 #DIGRAPHS_UnbindVariables
 gap> Unbind(a);