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2 minor fixes, including for the bug reported by macaj@dcs.fmph.uniba.sk #622

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Merged
fingolfin merged 3 commits into from
Feb 21, 2016
Merged

2 minor fixes, including for the bug reported by macaj@dcs.fmph.uniba.sk #622

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35debed
FIX: Zero element in Groebner basis computation
hulpke Feb 12, 2016
d6ccb99
COPY to 4.8: Clarify persistence of ordering in action homomorphisms.
hulpke Feb 13, 2016
05c6d5d
FIX (only): Catch misprint and unapplicable case in rare branch.
hulpke Feb 21, 2016
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6 changes: 4 additions & 2 deletions lib/clashom.gi
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Expand Up @@ -1807,7 +1807,7 @@ local classes, # classes to be constructed, the result
img:=orb[vp+j]*mats[genum];
#if img in orb then Error("HUH");fi;
Add(orb,img);
Add(reps,reps[vp+j]*mats[genum]);
Add(reps,reps[vp+j]*gens[genum]);
# repword stays the same!
Add(repwords,repword);
od;
Expand Down Expand Up @@ -1943,13 +1943,15 @@ BindGlobal("LiftClassesEATrivRep",
subs:=MTX.Homomorphisms(subs,mo);
orbsub:=Filtered(subs,x->x in orbsub);
fi;
if Length(orbsub)*Length(bas)=Length(bas[1]) then
if Length(orbsub)*Length(bas)=Length(bas[1]) and
RankMat(Concatenation(orbsub))=Length(bas[1]) then
found:=ssd;
el:=[orbsub,bas,fasize,nsgens,nsimgs,nsfgens,mo];

subs:=List([1..Length(orbsub)],x->[(x-1)*ssd+1..x*ssd]);
bas:=ImmutableMatrix(field,Concatenation(orbsub)); # this is the new basis
basinv:=bas^-1;
Assert(1,basinv<>fail);
else
Info(InfoHomClass,3,"failed ",Length(orbsub));
fi;
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2 changes: 1 addition & 1 deletion lib/groebner.gi
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Expand Up @@ -971,7 +971,7 @@ BindGlobal("GAPGBASIS",`rec(
GroebnerBasis:=function(elms,order)
local orderext, bas, baslte, fam, t, B, i, j, s;
orderext:=MonomialExtrepComparisonFun(order);
bas:=ShallowCopy(elms);
bas:=Filtered(elms,x->not IsZero(x));
baslte:=List(bas,ExtRepPolynomialRatFun);
fam:=FamilyObj(bas[1]);
baslte:=List(baslte,i->i[LeadingMonomialPosExtRep(fam,i,orderext)]);
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4 changes: 3 additions & 1 deletion lib/oprt.gd
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Expand Up @@ -898,7 +898,9 @@ end );
## <Description>
## computes a homomorphism from <A>G</A> into the symmetric group on
## <M>|<A>Omega</A>|</M> points that gives the permutation action of
## <A>G</A> on <A>Omega</A>.
## <A>G</A> on <A>Omega</A>. (In particular, this homomorphism is a
## permutation equivalence, that is the permutation image of a group element
## is given by the positions of points in <A>Omega</A>.)
## <P/>
## By default the homomorphism returned by
## <Ref Func="ActionHomomorphism" Label="for a group, an action domain, etc."/>
Expand Down