Add FolkmanGraph

gap/examples.gd

@@ -90,3 +90,7 @@ DeclareOperation("TadpoleDigraph", [IsFunction, IsPosInt, IsPosInt]);
 DeclareConstructor("BookDigraphCons", [IsDigraph, IsPosInt]);
 DeclareOperation("BookDigraph", [IsPosInt]);
 DeclareOperation("BookDigraph", [IsFunction, IsPosInt]);
+
+DeclareConstructor("FolkmanGraphCons", [IsDigraph]);
+DeclareOperation("FolkmanGraph", []);
+DeclareOperation("FolkmanGraph", [IsFunction]);

gap/examples.gi

@@ -711,6 +711,21 @@ function(filt, m, n)
   return D;
 end);
 
+InstallMethod(FolkmanGraphCons, "for IsMutableDigraph", [IsMutableDigraph],
+function(filt)
+  return DigraphFromGraph6String(IsMutableDigraph,
+                                 "Sl?gHS?_g?oTS?AA_?GOT@O??_i_?G@@S");
+end);
+
+InstallMethod(FolkmanGraphCons, "for IsImmutableDigraph", [IsImmutableDigraph],
+filt -> MakeImmutable(FolkmanGraphCons(IsMutableDigraph)));
+
+InstallMethod(FolkmanGraph, [],
+{} -> FolkmanGraphCons(IsImmutableDigraph));
+
+InstallMethod(FolkmanGraph, "for a function", [IsFunction],
+filt -> FolkmanGraphCons(filt));
+
 InstallMethod(BookDigraphCons,
 "for IsMutableDigraph and one positive integer",
 [IsMutableDigraph, IsPosInt],

tst/standard/examples.tst

@@ -228,6 +228,28 @@ Error, the arguments <n> and <k> must be non-negative integers,
 gap> JohnsonDigraph(IsMutableDigraph, 4, 2);
 <mutable digraph with 6 vertices, 24 edges>
 
+#  Folkman
+gap> D := FolkmanGraph();
+<immutable digraph with 20 vertices, 80 edges>
+gap> DigraphNrVertices(D) = 20;
+true
+gap> DigraphNrEdges(D) = 80;
+true
+gap> Size(AutomorphismGroup(D)) = 3840;
+true
+gap> IsHamiltonianDigraph(D);
+true
+gap> ChromaticNumber(D);
+2
+gap> DigraphDiameter(D);
+4
+gap> IsBipartiteDigraph(D);
+true
+gap> IsRegularDigraph(D);
+true
+gap> D := FolkmanGraph(IsMutableDigraph);
+<mutable digraph with 20 vertices, 80 edges>
+
 # LollipopGraph
 gap> LollipopGraph(5, 4);
 <immutable connected symmetric digraph with 9 vertices, 28 edges>