Add TadpoleDigraph

doc/examples.xml

@@ -309,3 +309,36 @@ gap> GeneralisedPetersenGraph(IsMutableDigraph, 9, 4);
   </Description>
 </ManSection>
 <#/GAPDoc>
+
+<#GAPDoc Label="TadpoleDigraph">
+<ManSection>
+  <Oper Name="TadpoleDigraph" Arg="[filt, ]m, n"/>
+  <Returns>A digraph.</Returns>
+  <Description>
+    If <A>m</A> and <A>n</A> are non-negative integers (where m > 2), then this operation
+    returns a Tadpole digraph.<P/>
+
+    If the optional first argument <A>filt</A> is present, then this should
+    specify the category or representation the digraph being created will
+    belong to. For example, if <A>filt</A> is <Ref Filt="IsMutableDigraph"/>,
+    then the digraph being created will be mutable, if <A>filt</A> is <Ref
+    Filt="IsImmutableDigraph"/>, then the digraph will be immutable. 
+    If the optional first argument <A>filt</A> is not present, then <Ref
+      Filt="IsImmutableDigraph"/> is used by default.<P/>
+
+    The <E>Tadpole digraph</E> consists of a cycle graph on m vertices and a path graph on
+    n vertices. These two graphs are connected by a bridge.<P/>
+
+    <Example><![CDATA[
+gap> TadpoleDigraph(10, 15);
+<immutable symmetric multidigraph with 25 vertices, 50 edges>
+gap> TadpoleDigraph(IsMutableDigraph, 5, 6);
+<mutable digraph with 11 vertices, 22 edges>
+gap> IsSymmetricDigraph(TadpoleDigraph(3, 5));
+true
+gap> IsMultiDigraph(TadpoleDigraph(3, 5));
+true
+]]></Example>
+  </Description>
+</ManSection>
+<#/GAPDoc>

gap/examples.gd

@@ -48,3 +48,7 @@ DeclareOperation("PetersenGraph", [IsFunction]);
 DeclareConstructor("GeneralisedPetersenGraphCons", [IsDigraph, IsInt, IsInt]);
 DeclareOperation("GeneralisedPetersenGraph", [IsInt, IsInt]);
 DeclareOperation("GeneralisedPetersenGraph", [IsFunction, IsInt, IsInt]);
+
+DeclareConstructor("TadpoleDigraphCons", [IsDigraph, IsInt, IsInt]);
+DeclareOperation("TadpoleDigraph", [IsInt, IsInt]);
+DeclareOperation("TadpoleDigraph", [IsFunction, IsInt, IsInt]);

gap/examples.gi

@@ -370,3 +370,58 @@ GeneralisedPetersenGraphCons);
 
 InstallMethod(GeneralisedPetersenGraph, "for integer, integer", [IsInt, IsInt],
 {n, k} -> GeneralisedPetersenGraphCons(IsImmutableDigraph, n, k));
+
+InstallMethod(GeneralisedPetersenGraphCons,
+"for IsImmutableDigraph, integer, int",
+[IsImmutableDigraph, IsInt, IsInt],
+function(filt, n, k)
+  local D;
+  D := MakeImmutable(GeneralisedPetersenGraphCons(IsMutableDigraph, n, k));
+  SetIsMultiDigraph(D, false);
+  SetIsSymmetricDigraph(D, true);
+  return D;
+end);
+
+InstallMethod(TadpoleDigraphCons, "for IsMutableDigraph and two integers",
+[IsMutableDigraph, IsInt, IsInt],
+function(filt, m, n)
+  local i, j, tail, graph;
+  if (m < 3) then
+    ErrorNoReturn("m needs to greater than 2");
+  elif (n < 0) then
+    ErrorNoReturn("n needs to be positive (or 0)");
+  fi;
+  graph := CycleDigraph(IsMutable, m);
+  DigraphAddEdge(graph, [1, m]);
+  for j in [2 .. m] do
+    DigraphAddEdge(graph, [j, j - 1]);
+  od;
+  if (n = 0) then
+    return graph;
+  fi;
+  tail := ChainDigraph(IsMutable, n);
+  for i in [2 .. n] do
+    DigraphAddEdge(tail, [i, i - 1]);
+  od;
+  DigraphDisjointUnion(graph, tail);
+  DigraphAddEdges(graph, [[m, n + m], [n + m, m]]);
+  return graph;
+end);
+
+InstallMethod(TadpoleDigraph, "for a function, integer, integer",
+[IsFunction, IsInt, IsInt],
+TadpoleDigraphCons);
+
+InstallMethod(TadpoleDigraph, "for integer, integer", [IsInt, IsInt],
+{m, n} -> TadpoleDigraphCons(IsImmutableDigraph, m, n));
+
+InstallMethod(TadpoleDigraphCons,
+"for IsImmutableDigraph, integer, integer",
+[IsImmutableDigraph, IsInt, IsInt],
+function(filt, m, n)
+  local D;
+  D := MakeImmutable(TadpoleDigraph(IsMutableDigraph, m, n));
+  SetIsMultiDigraph(D, true);
+  SetIsSymmetricDigraph(D, true);
+  return D;
+end);

tst/standard/examples.tst

@@ -226,6 +226,18 @@ Error, the arguments <n> and <k> must be non-negative integers,
 gap> JohnsonDigraph(IsMutableDigraph, 4, 2);
 <mutable digraph with 6 vertices, 24 edges>
 
-#
+# TadPoleDigraph
+gap> TadpoleDigraph(2, 2);
+Error, m needs to greater than 2
+gap> TadpoleDigraph(3, -1);
+Error, n needs to be positive (or 0)
+gap> TadpoleDigraph(10, 15);
+<immutable symmetric multidigraph with 25 vertices, 50 edges>
+gap> TadpoleDigraph(IsMutableDigraph, 5, 6);
+<mutable digraph with 11 vertices, 22 edges>
+gap> IsSymmetricDigraph(TadpoleDigraph(3, 5));
+true
+gap> IsMultiDigraph(TadpoleDigraph(3, 5));
+true
 gap> DIGRAPHS_StopTest();
 gap> STOP_TEST("Digraphs package: standard/examples.tst", 0);