let trivial_character set the irreducibility flag

some examples in invariant theory should get faster

(set the flag also in `linear_characters`)

src/GAP/wrappers.jl

@@ -349,6 +349,7 @@ GAP.@wrap RootSystem(x::GapObj)::GapObj
 GAP.@wrap ScalarProduct(x::GapObj, y::GapObj, z::GapObj)::GAP.Obj
 GAP.@wrap SchurIndexByCharacter(x::GapObj, y::GapObj, z::GapObj)::GAP.Obj
 GAP.@wrap Set(x::GapObj)::GapObj
+GAP.@wrap SetIsIrreducibleCharacter(x::Any, y::Bool)::Nothing
 GAP.@wrap SetMaximalAbelianQuotient(x::Any, y::Any)::Nothing
 GAP.@wrap SetSize(x::Any, y::Any)::Nothing
 GAP.@wrap ShrinkRowVector(x::GapObj)::Nothing
@@ -374,6 +375,7 @@ GAP.@wrap Symmetrizations(x::GapObj, y::GapObj, z::GapInt)::GapObj
 GAP.@wrap SymplecticComponents(x::GapObj, y::GapObj, z::GapInt)::GapObj
 GAP.@wrap TableOfMarks(x::GapObj)::GapObj
 GAP.@wrap Trace(x::GapObj, y::GAP.Obj)::GAP.Obj
+GAP.@wrap TrivialCharacter(x::GapObj)::GapObj
 GAP.@wrap UnderlyingElement(x::GapObj)::GapObj
 GAP.@wrap UnderlyingGroup(x::GapObj)::GapObj
 GAP.@wrap UnderlyingRingElement(x::GapObj)::GapObj

src/Groups/group_characters.jl

@@ -1978,8 +1978,9 @@ true
 ```
 """
 function trivial_character(tbl::GAPGroupCharacterTable)
-    val = QQAbFieldElem(1)
-    return class_function(tbl, [val for i in 1:ncols(tbl)])
+    triv = GAPWrap.TrivialCharacter(GapObj(tbl))
+    GAPWrap.SetIsIrreducibleCharacter(triv, true)
+    return class_function(tbl, triv)
 end
 
 @doc raw"""
@@ -1997,8 +1998,9 @@ true
 ```
 """
 function trivial_character(G::GAPGroup)
-    val = QQAbFieldElem(1)
-    return class_function(G, [val for i in 1:Int(number_of_conjugacy_classes(G))])
+    triv = GAPWrap.TrivialCharacter(GapObj(G))
+    GAPWrap.SetIsIrreducibleCharacter(triv, true)
+    return class_function(G, triv)
 end
 
 @doc raw"""
@@ -2201,10 +2203,13 @@ julia> length(linear_characters(tbl))
 ```
 """
 function linear_characters(tbl::GAPGroupCharacterTable)
-    return [class_function(tbl, chi) for chi in GAPWrap.LinearCharacters(GapObj(tbl))]
+    lin = GAPWrap.LinearCharacters(GapObj(tbl))
+    for chi in lin
+      GAPWrap.SetIsIrreducibleCharacter(chi, true)
+    end
+    return [class_function(tbl, chi) for chi in lin]
 end
 
-
 @doc raw"""
     induce(chi::GAPGroupClassFunction, G::Union{GAPGroup, FinGenAbGroup})
     induce(chi::GAPGroupClassFunction, tbl::GAPGroupCharacterTable[, fusion::Vector{Int}])