Fix cocycle and coboundary computation for trivial algebra modules

Reported by Rudolf Tange
gap-system · Jan 4, 2018 · 9ad2283 · 9ad2283
1 parent 105d625
commit 9ad2283
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Showing 2 changed files with 75 additions and 2 deletions.
diff --git a/lib/lierep.gi b/lib/lierep.gi
@@ -123,6 +123,14 @@ InstallMethod( CochainSpace,
  r:= Dimension( V );
  F:= LeftActingDomain( L );
 
+ if r = 0 then
+ if s = 0 then
+ return VectorSpace( F, [], Cochain( V, 0, Zero(V) ), "basis" );
+ else
+ return VectorSpace( F, [], Cochain( V, s, [] ), "basis" );
+ fi;
+ fi;
+
  if s = 0 then
  bas:= List( BasisVectors( Basis( V ) ), x -> Cochain( V, s, x ) );
  return VectorSpace( F, bas, "basis" );
@@ -623,7 +631,7 @@ InstallMethod( Coboundaries,
 
  if s = 0 then
  return VectorSpace( LeftActingDomain(V),
- [ Cochain( V, 0, Zero(V) ) ] );
+ [ ], Cochain( V, 0, Zero(V) ), "basis" );
  fi;
 
  # The s-coboundaries are the images of the (s-1)-cochains under
@@ -632,7 +640,10 @@ InstallMethod( Coboundaries,
  Csm1:= CochainSpace( V, s-1 );
  gens:= List( GeneratorsOfLeftModule( Csm1 ), x ->
  LieCoboundaryOperator(x) );
-
+ if Length(gens) = 0 then
+ return VectorSpace( LeftActingDomain(V),
+ [ ], Cochain( V, s, [] ), "basis" );
+ fi;
  return VectorSpace( LeftActingDomain(V), gens );
 
 end );
@@ -649,6 +660,7 @@ InstallMethod( Cocycles,
  # when restricted to the space of s-cochains.
 
  Cs:= CochainSpace( V, s );
+ if IsTrivial(Cs) then return Cs; fi;
  gens:= List( GeneratorsOfLeftModule( Cs ), x ->
  LieCoboundaryOperator(x) );
 

diff --git a/tst/testinstall/algrep.tst b/tst/testinstall/algrep.tst
@@ -54,5 +54,66 @@ gap> Dimension(S1);
 gap> S1:=SubAlgebraModule(S,bas,"basis");
 <16-dimensional left-module over <Lie algebra of dimension 4 over GF(3)>>
 
+#
+#
+# cocycles etc.
+#
+
+# for zero module
+gap> CochainSpace(S0,0);
+<vector space of dimension 0 over GF(3)>
+gap> CochainSpace(S0,1);
+<vector space of dimension 0 over GF(3)>
+gap> CochainSpace(S0,2);
+<vector space of dimension 0 over GF(3)>
+gap> Cocycles(S0,0);
+<vector space of dimension 0 over GF(3)>
+gap> Cocycles(S0,1);
+<vector space of dimension 0 over GF(3)>
+gap> Cocycles(S0,2);
+<vector space of dimension 0 over GF(3)>
+gap> Coboundaries(S0,0);
+<vector space of dimension 0 over GF(3)>
+gap> Coboundaries(S0,1);
+<vector space of dimension 0 over GF(3)>
+gap> Coboundaries(S0,2);
+<vector space of dimension 0 over GF(3)>
+
+# for proper submodule
+gap> CochainSpace(S1,0);
+<vector space of dimension 16 over GF(3)>
+gap> CochainSpace(S1,1);
+<vector space of dimension 64 over GF(3)>
+gap> CochainSpace(S1,2);
+<vector space of dimension 96 over GF(3)>
+gap> Cocycles(S1,0);
+<vector space of dimension 4 over GF(3)>
+gap> Cocycles(S1,1);
+<vector space of dimension 16 over GF(3)>
+gap> Cocycles(S1,2);
+<vector space of dimension 48 over GF(3)>
+gap> tmp:=Coboundaries(S1,0);; Dimension(tmp);; tmp;
+<vector space of dimension 0 over GF(3)>
+gap> tmp:=Coboundaries(S1,1);; Dimension(tmp);; tmp;
+<vector space of dimension 12 over GF(3)>
+gap> tmp:=Coboundaries(S1,2);; Dimension(tmp);; tmp;
+<vector space of dimension 48 over GF(3)>
+
+# for full module
+gap> CochainSpace(S,0);
+<vector space of dimension 35 over GF(3)>
+gap> CochainSpace(S,1);
+<vector space of dimension 140 over GF(3)>
+gap> CochainSpace(S,2);
+<vector space of dimension 210 over GF(3)>
+gap> Cocycles(S,0);
+<vector space of dimension 6 over GF(3)>
+gap> Cocycles(S,1);
+<vector space of dimension 45 over GF(3)>
+gap> tmp:=Coboundaries(S,0);; Dimension(tmp);; tmp;
+<vector space of dimension 0 over GF(3)>
+gap> tmp:=Coboundaries(S,1);; Dimension(tmp);; tmp;
+<vector space of dimension 29 over GF(3)>
+
 #
 gap> STOP_TEST( "algrep.tst", 1);