Added IsOrderFilter

doc/oper.xml

@@ -2414,14 +2414,12 @@ gap> List(res[2][3]);
     order defined by <A>D</A>. The function can only be used on digraphs
     satisfying <Ref Prop="IsPartialOrderDigraph"/> and will throw an error if
     passed a digraph that is not a partial order digraph.
-
     <Example><![CDATA[
 gap> D1 := Digraph([[1, 3], [2, 3], [3]]);
 <immutable digraph with 3 vertices, 5 edges>
-<immutable digraph with 3 vertices, 5 edges>
-gap> IsOrderIdeal(D, [1, 2, 3]);
+gap> IsOrderIdeal(D1, [1, 2, 3]);
 true
-gap> D2 := DigraphDisjointUnion(D, D);
+gap> D2 := DigraphDisjointUnion(D1, D1);
 <immutable digraph with 6 vertices, 10 edges>
 gap> IsOrderIdeal(D2, [1, 2, 3]);
 true
@@ -2432,6 +2430,29 @@ false
 ]]></Example>
   </Description>
 </ManSection>
+<#/GAPDoc>
+
+<#GAPDoc Label="IsOrderFilter">
+<ManSection>
+  <Oper Name="IsOrderFilter" Arg="D, subset" Label="for a digraph and a list"/>
+  <Returns> <K>true</K> or <K>false</K>.</Returns>
+  <Description>
+  This function returns <K>true</K> if the specified subset is upwards
+    closed. A subset is upwards closed if it contains every vertex greater than the given vertices in the
+    order defined by <A>D</A>. The function can only be used on digraphs
+    satisfying <Ref Prop="IsPartialOrderDigraph"/> and will throw an error if
+    passed a digraph that is not a partial order digraph. 
+    <Example><![CDATA[gap> D1 := DigraphByEdges(
+> [[1, 2], [2, 3], [1, 3], [1, 1], [2, 2], [3, 3]]);
+<immutable digraph with 3 vertices, 6 edges>
+gap> IsOrderFilter(D1, [2, 3]);
+false
+gap> IsOrderFilter(D1, [1, 2]);
+true]]>    
+    </Example>
+  </Description>
+</ManSection>
+<#/GAPDoc>
 
 <#GAPDoc Label="DIGRAPHS_FREE_HOMOS_DATA">
   <Oper Name="DIGRAPHS_FREE_HOMOS_DATA"/>

doc/z-chap5.xml

@@ -36,6 +36,8 @@
     <#Include Label="IsPartialOrderDigraph">
     <#Include Label="IsMeetSemilatticeDigraph">
     <#Include Label="DigraphMeetTable">
+    <#Include Label="IsOrderIdeal">
+    <#Include Label="IsOrderFilter">
     <#Include Label="IsUpperSemimodularDigraph">
     <#Include Label="IsDistributiveLatticeDigraph">
     <#Include Label="IsModularLatticeDigraph">

gap/oper.gd

@@ -142,6 +142,7 @@ DeclareOperation("DigraphShortestPathSpanningTree", [IsDigraph, IsPosInt]);
 DeclareOperation("VerticesReachableFrom", [IsDigraph, IsPosInt]);
 DeclareOperation("VerticesReachableFrom", [IsDigraph, IsList]);
 DeclareOperation("IsOrderIdeal", [IsDigraph, IsList]);
+DeclareOperation("IsOrderFilter", [IsDigraph, IsList]);
 DeclareOperation("Dominators", [IsDigraph, IsPosInt]);
 DeclareOperation("DominatorTree", [IsDigraph, IsPosInt]);
 DeclareOperation("DigraphCycleBasis", [IsDigraph]);

gap/oper.gi

@@ -2312,6 +2312,10 @@ function(D, roots)
 
 end);
 
+InstallMethod(IsOrderFilter, "for a digraph and a list of vertices",
+[IsDigraph, IsList],
+{D, roots} -> IsOrderIdeal(DigraphReverse(D), roots));
+
 InstallMethod(DominatorTree, "for a digraph and a vertex",
 [IsDigraph, IsPosInt],
 function(D, root)
@@ -2543,8 +2547,8 @@ function(G)
   c := Length(unusedEdges);
 
   # Warning for large matrix
-  # The warning is printed roughly when the result matrix will take up
-  # more than 8GB of RAM.
+  # The warning is printed roughly when the result matrix will
+  # take up more than 8GB of RAM.
   if (10 ^ 11) / 2 < m * c then
     Info(InfoWarning, 1, StringFormatted(
     "The resulting matrix is going to be large of size {} \x {} ",

tst/standard/oper.tst

@@ -2843,6 +2843,27 @@ gap> D := CycleDigraph(5);;
 gap> IsOrderIdeal(D, [1]);
 Error, the 1st argument (a digraph) must be a partial order digraph
 
+# IsOrderFilter
+gap> D := DigraphByEdges([[1, 1], [1, 2], [1, 3], [2, 3], [3, 3], [2, 2], [2, 4], [4, 4], [1, 4]]);
+<immutable digraph with 4 vertices, 9 edges>
+gap> IsOrderFilter(D, [1, 2]);
+true
+gap> IsOrderFilter(D, [2, 3]);
+false
+gap> IsOrderFilter(D, [1, 4]);
+false
+gap> IsOrderFilter(D, [4]);
+false
+gap> IsOrderFilter(4);
+Error, no method found! For debugging hints type ?Recovery from NoMethodFound
+Error, no 1st choice method found for `IsOrderFilter' on 1 arguments
+gap> IsOrderFilter(D, 4);
+Error, no method found! For debugging hints type ?Recovery from NoMethodFound
+Error, no 1st choice method found for `IsOrderFilter' on 2 arguments
+gap> IsOrderFilter(D, [5]);
+Error, an element of the 2nd argument (roots) is not a vertex of the 1st argum\
+ent (a digraph)
+
 # DigraphCycleBasis
 gap> D := NullDigraph(0);
 <immutable empty digraph with 0 vertices>