Add NrAdjacencies

digraphs · Sep 2, 2024 · f4b45f0 · f4b45f0
1 parent 4e2bc04
commit f4b45f0
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Showing 4 changed files with 38 additions and 0 deletions.
diff --git a/gap/attr.gd b/gap/attr.gd
@@ -14,6 +14,7 @@ DeclareAttribute("DigraphVertices", IsDigraph);
 DeclareAttribute("DigraphNrVertices", IsDigraph);
 DeclareAttribute("DigraphEdges", IsDigraph);
 DeclareAttribute("DigraphNrEdges", IsDigraph);
+DeclareAttribute("DigraphNrAdjacencies", IsDigraph);
 DeclareAttribute("DigraphNrLoops", IsDigraph);
 DeclareAttribute("DigraphHash", IsDigraph);
 

diff --git a/gap/attr.gi b/gap/attr.gi
@@ -701,6 +701,13 @@ function(D)
   return m;
 end);
 
+InstallMethod(DigraphNrAdjacencies, "for a digraph", [IsDigraphByOutNeighboursRep],
+function(D)
+  local m;
+  m := DIGRAPH_NRADJACENCIES(D);
+  return m;
+end);
+
 InstallMethod(DigraphNrLoops,
 "for a digraph by out-neighbours",
 [IsDigraphByOutNeighboursRep],

diff --git a/src/digraphs.c b/src/digraphs.c
@@ -138,6 +138,34 @@ static Obj FuncDIGRAPH_NREDGES(Obj self, Obj D) {
   return INTOBJ_INT(DigraphNrEdges(D));
 }
 
+Int DigraphNrAdjacencies(Obj D) {
+  Int nr = 0;
+  if (IsbPRec(D, RNamName("DigraphNrAdjacencies"))) {
+    return INT_INTOBJ(ElmPRec(D, RNamName("DigraphNrAdjacencies")));
+  } else {
+    Obj const out = FuncOutNeighbours(0L, D);
+    for (Int v = 1; v <= LEN_LIST(out); ++v) {
+      Obj const out_v = ELM_LIST(out, v);
+      for (Int w = 1; w <= LEN_LIST(out_v); ++w) {
+        Int u = INT_INTOBJ(ELM_LIST(out_v, w));
+        if (v < u
+            || CALL_3ARGS(IsDigraphEdge, D, INTOBJ_INT(u), INTOBJ_INT(v))
+                   == False) {
+          ++nr;
+        }
+      }
+    }
+  }
+  if (IsAttributeStoringRep(D)) {
+    AssPRec(D, RNamName("DigraphNrAdjacencies"), INTOBJ_INT(nr));
+  }
+  return nr;
+}
+
+static Obj FuncDIGRAPH_NRADJACENCIES(Obj self, Obj D) {
+  return INTOBJ_INT(DigraphNrAdjacencies(D));
+}
+
 /****************************************************************************
 **
 *F  FuncGABOW_SCC
@@ -2113,6 +2141,7 @@ FuncMULTIDIGRAPH_CANONICAL_LABELLING(Obj self, Obj digraph, Obj colours) {
 
 static StructGVarFunc GVarFuncs[] = {
     GVAR_FUNC(DIGRAPH_NREDGES, 1, "digraph"),
+    GVAR_FUNC(DIGRAPH_NRADJACENCIES, 1, "digraph"),
     GVAR_FUNC(GABOW_SCC, 1, "adj"),
     GVAR_FUNC(DIGRAPH_CONNECTED_COMPONENTS, 1, "digraph"),
     GVAR_FUNC(IS_ACYCLIC_DIGRAPH, 1, "adj"),

diff --git a/src/digraphs.h b/src/digraphs.h
@@ -24,6 +24,7 @@ Obj FuncIS_ANTISYMMETRIC_DIGRAPH(Obj self, Obj D);
 Obj FuncADJACENCY_MATRIX(Obj self, Obj D);
 
 Int DigraphNrEdges(Obj digraph);
+Int DigraphNrAdjacencies(Obj digraph);
 Obj DigraphSource(Obj digraph);
 Obj DigraphRange(Obj digraph);