From e5bf02f9c34ca3ee50956e796f658a771cb4da37 Mon Sep 17 00:00:00 2001
From: "James D. Mitchell" <jdm3@st-andrews.ac.uk>
Date: Wed, 20 Jan 2021 15:16:43 +0000
Subject: [PATCH] Add FolkmanGraph

---
 gap/examples.gd           |  4 ++++
 gap/examples.gi           | 15 +++++++++++++++
 tst/standard/examples.tst | 22 ++++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/gap/examples.gd b/gap/examples.gd
index 406ac18ae..750dd4201 100644
--- a/gap/examples.gd
+++ b/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]);
diff --git a/gap/examples.gi b/gap/examples.gi
index bd916be38..e7d9a97a6 100644
--- a/gap/examples.gi
+++ b/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],
diff --git a/tst/standard/examples.tst b/tst/standard/examples.tst
index 8ede44549..03d563a40 100644
--- a/tst/standard/examples.tst
+++ b/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>