Merge branch 'bellmanford' of https://github.com/baydrea/Digraphs into bellmanford

Author: baydrea

doc/oper.xml

@@ -257,6 +257,56 @@ gap> OutNeighbours(D2);
 </ManSection>
 <#/GAPDoc>
 
+<#GAPDoc Label="OnTuplesDigraphs">
+<ManSection>
+  <Oper Name="OnTuplesDigraphs" Arg="list, perm"
+    Label="for a list of digraphs and a perm"/>
+  <Oper Name="OnSetsDigraphs" Arg="list, perm"
+    Label="for a set of digraphs and a perm"/>
+  <Returns>A list or set of digraphs.</Returns>
+  <Description>
+    If <A>list</A> is a list of digraphs, and <A>perm</A> is a
+    <E>permutation</E> of the vertices of the digraphs in <A>list</A>, then
+    <Ref Oper="OnTuplesDigraphs" Label="for a list of digraphs and a perm"/>
+    returns a new list constructed by applying <A>perm</A> via
+    <Ref Oper="OnDigraphs" Label="for a digraph and a perm"/>
+    to a copy (with the same mutability) of each entry of <A>list</A> in turn.
+    <P/>
+
+    More precisely, <C>OnTuplesDigraphs(<A>list</A>,<A>perm</A>)</C> is a list
+    of length <C>Length(<A>list</A>)</C>, whose <C>i</C>-th entry is
+    <C>OnDigraphs(DigraphCopy(<A>list</A>[i]), <A>perm</A>)</C>.
+    <P/>
+
+    If <A>list</A> is moreover a &GAP; set (i.e. a duplicate-free sorted list),
+    then <Ref Oper="OnSetsDigraphs" Label="for a set of digraphs and a perm"/>
+    returns the sorted output of
+    <Ref Oper="OnTuplesDigraphs" Label="for a list of digraphs and a perm"/>,
+    which is therefore again a set.
+    <Example><![CDATA[
+gap> list := [CycleDigraph(IsMutableDigraph, 6),
+>             DigraphReverse(CycleDigraph(6))];
+[ <mutable digraph with 6 vertices, 6 edges>, 
+  <immutable digraph with 6 vertices, 6 edges> ]
+gap> p := (1, 6)(2, 5)(3, 4);;
+gap> result_tuples := OnTuplesDigraphs(list, p);
+[ <mutable digraph with 6 vertices, 6 edges>, 
+  <immutable digraph with 6 vertices, 6 edges> ]
+gap> result_tuples[2] = OnDigraphs(list[2], p);
+true
+gap> result_tuples = list;
+false
+gap> result_tuples = Reversed(list);
+true
+gap> result_sets := OnSetsDigraphs(list, p);
+[ <immutable digraph with 6 vertices, 6 edges>, 
+  <mutable digraph with 6 vertices, 6 edges> ]
+gap> result_sets = list;
+true]]></Example>
+  </Description>
+</ManSection>
+<#/GAPDoc>
+
 <#GAPDoc Label="DigraphAddVertex">
 <ManSection>
   <Oper Name="DigraphAddVertex" Arg="digraph[, label ]"/>

doc/prop.xml

@@ -717,7 +717,8 @@ false
     <K>false</K> if it is not. A digraph is <E>empty</E> if it has no
     edges.<P/>
 
-    <C>IsNullDigraph</C> is a synonym for <C>IsEmptyDigraph</C>.
+    <Ref Prop="IsNullDigraph"/> is a synonym for <Ref Prop="IsEmptyDigraph"/>.
+    See also <Ref Prop="IsNonemptyDigraph"/>.
     <P/>
 
     &MUTABLE_RECOMPUTED_PROP;
@@ -739,6 +740,93 @@ false]]></Example>
 </ManSection>
 <#/GAPDoc>
 
+<#GAPDoc Label="IsNonemptyDigraph">
+<ManSection>
+  <Prop Name="IsNonemptyDigraph" Arg="digraph"/>
+  <Returns><K>true</K> or <K>false</K>.</Returns>
+  <Description>
+    Returns <K>true</K> if the digraph <A>digraph</A> is nonempty, and
+    <K>false</K> if it is not. A digraph is <E>nonempty</E> if it has at
+    least one edge.<P/>
+
+    See also <Ref Prop="IsEmptyDigraph"/>.
+    <P/>
+
+    &MUTABLE_RECOMPUTED_PROP;
+
+    <Example><![CDATA[
+gap> D := Digraph([[], []]);
+<immutable empty digraph with 2 vertices>
+gap> IsNonemptyDigraph(D);
+false
+gap> D := Digraph([[], [1]]);
+<immutable digraph with 2 vertices, 1 edge>
+gap> IsNonemptyDigraph(D);
+true]]></Example>
+  </Description>
+</ManSection>
+<#/GAPDoc>
+
+<#GAPDoc Label="DigraphHasAVertex">
+<ManSection>
+  <Prop Name="DigraphHasAVertex" Arg="digraph"/>
+  <Returns><K>true</K> or <K>false</K>.</Returns>
+  <Description>
+    Returns <K>true</K> if the digraph <A>digraph</A> has at least one vertex,
+    and <K>false</K> if it does not.<P/>
+
+    See also <Ref Prop="DigraphHasNoVertices"/>.
+    <P/>
+
+    &MUTABLE_RECOMPUTED_PROP;
+
+    <Example><![CDATA[
+gap> D := Digraph([]);
+<immutable empty digraph with 0 vertices>
+gap> DigraphHasAVertex(D);
+false
+gap> D := Digraph([[]]);
+<immutable empty digraph with 1 vertex>
+gap> DigraphHasAVertex(D);
+true
+gap> D := Digraph([[], [1]]);
+<immutable digraph with 2 vertices, 1 edge>
+gap> DigraphHasAVertex(D);
+true]]></Example>
+  </Description>
+</ManSection>
+<#/GAPDoc>
+
+<#GAPDoc Label="DigraphHasNoVertices">
+<ManSection>
+  <Prop Name="DigraphHasNoVertices" Arg="digraph"/>
+  <Returns><K>true</K> or <K>false</K>.</Returns>
+  <Description>
+    Returns <K>true</K> if the digraph <A>digraph</A> is the unique digraph
+    with zero vertices, and <K>false</K> otherwise.<P/>
+
+    See also <Ref Prop="DigraphHasAVertex"/>.
+    <P/>
+
+    &MUTABLE_RECOMPUTED_PROP;
+
+    <Example><![CDATA[
+gap> D := Digraph([]);
+<immutable empty digraph with 0 vertices>
+gap> DigraphHasNoVertices(D);
+true
+gap> D := Digraph([[]]);
+<immutable empty digraph with 1 vertex>
+gap> DigraphHasNoVertices(D);
+false
+gap> D := Digraph([[], [1]]);
+<immutable digraph with 2 vertices, 1 edge>
+gap> DigraphHasNoVertices(D);
+false]]></Example>
+  </Description>
+</ManSection>
+<#/GAPDoc>
+
 <#GAPDoc Label="IsEulerianDigraph">
 <ManSection>
   <Prop Name="IsEulerianDigraph" Arg="digraph"/>

doc/z-chap5.xml

@@ -1,5 +1,10 @@
 <Chapter Label="Properties of digraphs"><Heading>Properties of digraphs</Heading>
 
+  <Section><Heading>Vertex properties</Heading>
+    <#Include Label="DigraphHasAVertex">
+    <#Include Label="DigraphHasNoVertices">
+  </Section>
+
   <Section><Heading>Edge properties</Heading>
     <#Include Label="DigraphHasLoops">
     <#Include Label="IsAntisymmetricDigraph">
@@ -12,6 +17,7 @@
     <#Include Label="IsFunctionalDigraph">
     <#Include Label="IsPermutationDigraph">
     <#Include Label="IsMultiDigraph">
+    <#Include Label="IsNonemptyDigraph">
     <#Include Label="IsReflexiveDigraph">
     <#Include Label="IsSymmetricDigraph">
     <#Include Label="IsTournament">

doc/z-chap6.xml

@@ -11,6 +11,7 @@ from} $E_a$ \emph{to} $E_b$. In this case we say that $E_a$ and $E_b$ are
   <Section><Heading>Acting on digraphs</Heading>
     <#Include Label="OnDigraphs">
     <#Include Label="OnMultiDigraphs">
+    <#Include Label="OnTuplesDigraphs">
   </Section>
 
   <Section Label="Isomorphisms and canonical labellings">

gap/attr.gi

@@ -1128,7 +1128,7 @@ function(D)
   # alter the answer for the diameter/girth if necessary.  This function is
   # called, if appropriate, by DigraphDiameter and DigraphUndirectedGirth.
 
-  if DigraphNrVertices(D) = 0 and IsImmutableDigraph(D) then
+  if DigraphHasNoVertices(D) and IsImmutableDigraph(D) then
     SetDigraphDiameter(D, fail);
     SetDigraphUndirectedGirth(D, infinity);
     return rec(diameter := fail, girth := infinity);
@@ -1539,10 +1539,10 @@ end);
 
 InstallMethod(DegreeMatrix, "for a digraph", [IsDigraph],
 function(D)
-  if DigraphNrVertices(D) = 0 then
-    return [];
+  if DigraphHasAVertex(D) then
+    return DiagonalMat(OutDegrees(D));
   fi;
-  return DiagonalMat(OutDegrees(D));
+  return [];
 end);
 
 InstallMethod(LaplacianMatrix, "for a digraph", [IsDigraph],
@@ -1863,7 +1863,7 @@ function(D)
     SetDigraphAddAllLoopsAttr(D, C);
     SetIsReflexiveDigraph(C, true);
     SetIsMultiDigraph(C, ismulti);
-    SetDigraphHasLoops(C, DigraphNrVertices(C) > 0);
+    SetDigraphHasLoops(C, DigraphHasAVertex(C));
   fi;
   return C;
 end);
@@ -2312,7 +2312,7 @@ InstallMethod(UndirectedSpanningForest, "for a digraph by out-neighbours",
 [IsDigraphByOutNeighboursRep],
 function(D)
   local C;
-  if DigraphNrVertices(D) = 0 then
+  if DigraphHasNoVertices(D) then
     return fail;
   fi;
   C := MaximalSymmetricSubdigraph(D)!.OutNeighbours;
@@ -2341,9 +2341,9 @@ InstallMethod(UndirectedSpanningForestAttr, "for an immutable digraph",
 InstallMethod(UndirectedSpanningTree, "for a mutable digraph",
 [IsMutableDigraph],
 function(D)
-  if DigraphNrVertices(D) = 0
-      or not IsStronglyConnectedDigraph(D)
-      or not IsConnectedDigraph(UndirectedSpanningForest(DigraphMutableCopy(D)))
+  if not (DigraphHasAVertex(D)
+      and IsStronglyConnectedDigraph(D)
+      and IsConnectedDigraph(UndirectedSpanningForest(DigraphMutableCopy(D))))
       then
     return fail;
   fi;
@@ -2357,7 +2357,7 @@ InstallMethod(UndirectedSpanningTreeAttr, "for an immutable digraph",
 [IsImmutableDigraph],
 function(D)
   local out;
-  if DigraphNrVertices(D) = 0
+  if DigraphHasNoVertices(D)
       or not IsStronglyConnectedDigraph(D)
       or (HasMaximalSymmetricSubdigraphAttr(D)
           and not IsStronglyConnectedDigraph(MaximalSymmetricSubdigraph(D)))

gap/digraph.gd

@@ -14,6 +14,7 @@ DeclareCategory("IsDigraphWithAdjacencyFunction", IsDigraph);
 DeclareCategory("IsCayleyDigraph", IsDigraph);
 DeclareCategory("IsImmutableDigraph", IsDigraph);
 DeclareSynonym("IsMutableDigraph", IsDigraph and IsMutable);
+DeclareCategoryCollections("IsDigraph");
 
 DeclareAttribute("DigraphMutabilityFilter", IsDigraph);
 

gap/digraph.gi

@@ -1065,7 +1065,7 @@ p -> AsDigraph(AsTransformation(p)));
 InstallMethod(AsBinaryRelation, "for a digraph", [IsDigraphByOutNeighboursRep],
 function(D)
   local rel;
-  if DigraphNrVertices(D) = 0 then
+  if DigraphHasNoVertices(D) then
     ErrorNoReturn("the argument <D> must be a digraph with at least 1 ",
                   "vertex,");
   elif IsMultiDigraph(D) then

gap/grahom.gi

@@ -107,9 +107,9 @@ function(D, n)
     fi;
   fi;
 
-  # Only the null D with 0 vertices can be coloured with 0 colours
+  # Only the null digraph with 0 vertices can be coloured with 0 colours
   if n = 0 then
-    if DigraphNrVertices(D) = 0 then
+    if DigraphHasNoVertices(D) then
       return IdentityTransformation;
     fi;
     return fail;

gap/isomorph.gi

@@ -142,7 +142,7 @@ if DIGRAPHS_NautyAvailable then
                                                  colors);
       colors := NautyColorData(colors);
     fi;
-    if DigraphNrVertices(D) = 0 then
+    if DigraphHasNoVertices(D) then
       # This circumvents Issue #17 in NautyTracesInterface, whereby a graph
       # with 0 vertices causes a seg fault.
       return [Group(()), ()];

gap/oper.gd

@@ -59,6 +59,8 @@ DeclareOperation("DIGRAPHS_GraphProduct", [IsDigraph, IsDigraph, IsFunction]);
 # 4. Actions . . .
 DeclareOperation("OnDigraphs", [IsDigraph, IsPerm]);
 DeclareOperation("OnDigraphs", [IsDigraph, IsTransformation]);
+DeclareOperation("OnTuplesDigraphs", [IsDigraphCollection, IsPerm]);
+DeclareOperation("OnSetsDigraphs", [IsDigraphCollection, IsPerm]);
 DeclareOperation("OnMultiDigraphs", [IsDigraph, IsPermCollection]);
 DeclareOperation("OnMultiDigraphs", [IsDigraph, IsPerm, IsPerm]);