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add DefaultFieldOfMatrix for IsAlgebraicElementCollColl #6182

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add DefaultFieldOfMatrix for IsAlgebraicElementCollColl #6182

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393acfc
add `DefaultFieldOfMatrix` for `IsAlgebraicElementCollColl`
ThomasBreuer Dec 18, 2025
ed88d9a
address comment
ThomasBreuer Dec 27, 2025
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17 changes: 17 additions & 0 deletions lib/matrix.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -1253,6 +1253,23 @@ function( mat )
end );


#############################################################################
##
#M DefaultFieldOfMatrix( <algext-mat> )
##
InstallMethod( DefaultFieldOfMatrix,
[ "IsMatrix and IsAlgebraicElementCollColl" ],
function( mat )
local fam;

fam:= ElementsFamily( ElementsFamily( FamilyObj( mat) ) );
if not IsBound( fam!.wholeExtension ) then
TryNextMethod();
fi;
return fam!.wholeExtension;
end );


#############################################################################
##
#M BaseDomain( <v> )
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4 changes: 4 additions & 0 deletions tst/testinstall/vecmat.tst
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Expand Up @@ -224,6 +224,10 @@ gap> m = w;
true
gap> IsMutable(w);
false
gap> DefaultFieldOfMatrix( m ) = F;
true
gap> CharacteristicPolynomial( m );
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@fingolfin fingolfin Dec 26, 2025

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Perhaps we should also add an explicit test of DefaultFieldOfMatrix(m) ?

x_1^3-!Z(3)^0

# identity matrix over a ring with zero divisors
gap> F := Integers mod 6;; m := IdentityMat( 3, F );
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