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Avoid BaseChangeHomomorphism #124

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Merged
fingolfin merged 1 commit into from
Nov 26, 2025
Merged

Avoid BaseChangeHomomorphism #124

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11 changes: 4 additions & 7 deletions gap/Forms.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ end);
# appropriate field.
InstallGlobalFunction("ConjugateToSesquilinearForm",
function(group, type, gramMatrix)
local gapForm, newForm, gapToCanonical, canonicalToNew, field, formMatrix,
local gapForm, newForm, baseChangeMatrix, field, formMatrix,
result, d, q, broadType;
if not type in ["S", "O-B", "O-Q", "U"] then
ErrorNoReturn("<type> must be one of 'S', 'U', 'O-B', 'O-Q'");
Expand Down Expand Up @@ -82,12 +82,9 @@ function(group, type, gramMatrix)
ErrorNoReturn("The form preserved by <group> must be similar to the form ",
"described by the Gram matrix <gramMatrix>.");
fi;
gapToCanonical := BaseChangeHomomorphism(BaseChangeToCanonical(gapForm),
field);
canonicalToNew := BaseChangeHomomorphism(BaseChangeToCanonical(newForm) ^ (-1),
field);
result := MatrixGroup(field, canonicalToNew(gapToCanonical(GeneratorsOfGroup(group))));

baseChangeMatrix := BaseChangeToCanonical(gapForm)^-1 * BaseChangeToCanonical(newForm);
result := MatrixGroup(field, List(GeneratorsOfGroup(group), g -> g ^ baseChangeMatrix));

# Set useful attributes
UseIsomorphismRelation(group, result);
else
Expand Down
4 changes: 3 additions & 1 deletion tst/standard/ExtraspecialNormalizerMatrixGroups.tst
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Expand Up @@ -134,7 +134,9 @@ gap> TestExtraspecialNormalizerInOmega := function(m, q)
> CheckIsSubsetOmega(1, 2 ^ m, q, G);
> CheckSize(G);
> end;;
gap> TestExtraspecialNormalizerInOmega(3, 3);
#@if IsBound(CLASSICAL_MAXIMALS_RUN_BROKEN_TESTS)
gap> TestExtraspecialNormalizerInOmega(3, 3); # FIXME: 'Error, the recognition described by this recognition node has failed!' or 'Error, This should never have happened (346), tell Max.'
#@fi
gap> TestExtraspecialNormalizerInOmega(3, 5);
gap> TestExtraspecialNormalizerInOmega(3, 7);
#@if IsBound(CLASSICAL_MAXIMALS_RUN_BROKEN_TESTS)
Expand Down
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