Fix bug in ValueMolienSeries

Fixes #300
gap-system · Feb 15, 2018 · 5e22239 · 5e22239
1 parent 64a2d86
commit 5e22239
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diff --git a/lib/ctblmoli.gi b/lib/ctblmoli.gi
@@ -547,6 +547,7 @@ InstallGlobalFunction( MolienSeries, function( arg )
                          rec( summands    := numers,
                               size        := Size( tbl ),
                               degree      := psi[1],
+                              pol         := pol,
                               numer       := numer,
                               denom       := denom,
                               denominfo   := denominfo,
@@ -683,6 +684,9 @@ InstallGlobalFunction( ValueMolienSeries, function( series, i )
     series:= MolienSeriesInfo( series );
     value:= Sum( series.summands,
                  s -> CoefficientTaylorSeries( s.numer, s.r, s.k, i ), 0 );
+    if i+1 <= Length( series.pol ) then
+      value:=value + series.pol[i+1];
+    fi;
 
     # There is a factor $\frac{(-1)^{\psi(1)}}{\|G\|}$.
     if series.degree mod 2 = 1 then

diff --git a/tst/testinstall/ctblmoli.tst b/tst/testinstall/ctblmoli.tst
@@ -6,6 +6,8 @@
 #Y  Copyright (C)  1997,  Lehrstuhl D für Mathematik,  RWTH Aachen,  Germany
 ##
 gap> START_TEST("ctblmoli.tst");
+
+#
 gap> G:= AlternatingGroup( 5 );;
 gap> psi:= First( Irr( G ), x -> Degree( x ) = 3 );;
 gap> molser:= MolienSeries( psi );
@@ -14,6 +16,8 @@ gap> List( [ 0 .. 20 ], i -> ValueMolienSeries( molser, i ) );
 [ 1, 0, 1, 0, 1, 0, 2, 0, 2, 0, 3, 0, 4, 0, 4, 1, 5, 1, 6, 1, 7 ]
 gap> MolienSeriesWithGivenDenominator( molser, [ 2, 6, 10 ] );
 ( 1+z^15 ) / ( (1-z^10)*(1-z^6)*(1-z^2) )
+
+#
 gap> y:= E(3);; x:= E(3)^2;;
 gap> G:= Group(
 >            [ [ 0, y, 0, 0, 0, 0 ],
@@ -30,6 +34,25 @@ gap> Size( G );
 9720
 gap> MolienSeries( NaturalCharacter( G ) );
 ( 1 ) / ( (1-z^12)*(1-z^9)*(1-z^6)*(1-z^5)*(1-z^3)*(1-z) )
+
+#
+# the following test comes from https://github.com/gap-system/gap/issues/300
+# this used to give a wrong value for ValueMolienSeries(m,0) of 26/27 instead
+# of the correct value 1
+#
+gap> g:=SymplecticGroup(6,3);;
+gap> h:=Stabilizer(g,Z(3)*[1,0,0,0,0,0]);;
+gap> t:=CharacterTable(h);;
+gap> chi:=Irr(t)[7];;
+gap> chi[1];
+9
+gap> m:=MolienSeries(t,chi);;
+gap> List( [ 0 .. 20 ], i -> ValueMolienSeries( m, i ) );
+[ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 5, 0, 0 ]
+gap> List( [ 0,3 .. 48 ], i -> ValueMolienSeries( m, i ) );
+[ 1, 0, 0, 0, 2, 0, 5, 0, 13, 3, 33, 15, 87, 58, 203, 178, 472 ]
+
+#
 gap> STOP_TEST( "ctblmoli.tst", 1);
 
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