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Fix parent of the generators of the ideal returned from groebner_basis_f4 when used with eliminate > 0 #5918

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Merged
fingolfin merged 5 commits into from
Apr 8, 2026
Merged

Fix parent of the generators of the ideal returned from groebner_basis_f4 when used with eliminate > 0 #5918

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44f7aaf
remove early return
antonydellavecchia Apr 7, 2026
fff7536
fix parent of gens and base_ring of ideal after f4 eliminate
antonydellavecchia Apr 7, 2026
dc77a2c
fixes for the other tests
antonydellavecchia Apr 8, 2026
9efaa9f
remove deprecated zeros function
antonydellavecchia Apr 8, 2026
3bc624d
fix test
antonydellavecchia Apr 8, 2026
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8 changes: 5 additions & 3 deletions src/Rings/groebner/f4.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -63,13 +63,15 @@ function groebner_basis_f4(
AI = AlgebraicSolving.Ideal(oscar_generators(I))
if eliminate == 0
AR = base_ring(I)
embedding = identity
else
vars = symbols(base_ring(I))[eliminate+1:end]
AR, = polynomial_ring(coefficient_ring(I), vars; cached=false)
embedding = hom(base_ring(I), AR, [[zero(AR) for _ in 1:eliminate]; gens(AR)])
end
ord = degrevlex(AR)
if length(AI.gens) == 0
GB = IdealGens(base_ring(I), singular_generators(I), complete_reduction)
GB = IdealGens(AR, [embedding(p) for p in singular_generators(I)], complete_reduction)
GB.ord = ord
GB..isGB = true
GB.S.isGB = true
Expand All @@ -84,8 +86,8 @@ function groebner_basis_f4(
normalize = normalize,
truncate_lifting = truncate_lifting,
info_level = info_level)

GB = IdealGens(AR, AI.gb[eliminate], ord, keep_ordering = false,
GB = IdealGens(AR, [embedding(p) for p in AI.gb[eliminate]], ord, keep_ordering = false,
isGB = true, isReduced = complete_reduction)
end
if eliminate == 0
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16 changes: 13 additions & 3 deletions test/Rings/groebner.jl
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Expand Up @@ -227,6 +227,7 @@ end
x3*x4^2 + 238609298*x4^3 + 14913081*x2*x4 + 56338306*x3*x4 + 129246702*x4^2 + 263464432*x2 + 260150414*x3 + 258493405*x4
x2*x4^2 + 89478486*x4^3 + 29826162*x2*x4 + 263464432*x3*x4 + 238609297*x4^2 + 141674270*x2 + 9942054*x3
x4^4 + 35851649*x4^3 + 232885084*x2*x4 + 251179133*x3*x4 + 231479137*x4^2 + 191484965*x2 + 85955250*x3 + 167408122*x4]

@test elements(H) == G
@test isdefined(I, :gb)
@test Oscar.oscar_generators(I.gb[degrevlex(gens(base_ring(I)))]) == G
Expand All @@ -236,14 +237,23 @@ end
x3^3 + 156877866*x3*x4^2 + 59264971*x4^3 + 224858274*x3^2 + 183605206*x3*x4 + 130731555*x4^2 + 110395535*x3 + 158620953*x4
x4^4 + 167618101*x3*x4^2 + 102789335*x4^3 + 193931678*x3^2 + 156155981*x3*x4 + 60823186*x4^2 + 239040667*x3 + 127377432*x4
x3*x4^3 + 99215126*x3*x4^2 + 261328123*x4^3 + 132228634*x3^2 + 93598185*x3*x4 + 85654356*x4^2 + 3613010*x3 + 240673711*x4]
@test elements(H) == G

emb = hom(R, base_ring(H), [[zero(base_ring(H)) for _ in 1:2]; gens(base_ring(H))])

@test elements(H) == map(emb, G)
@test length(I.gb) == 1
# issue 5216
R, (a,b,c,d,x,y,z,w) = polynomial_ring(QQ, ["a", "b", "c", "d", "x", "y", "z", "w"])
I = ideal(R, [x - a*c, y - a*c*d, z - a*c^2 - b, w - a*c^2*d - b*d])
H = groebner_basis_f4(I; eliminate=4);
G= [-x*w + y*z]
@test elements(H) == G
G = [-x * w + y * z]
emb = hom(R, base_ring(H), [[zero(base_ring(H)) for _ in 1:4]; gens(base_ring(H))])
@test elements(H) == map(emb, G)
@test parent(first(gens(H))) == base_ring(H)

I = ideal(R, [zero(R)])
H = groebner_basis_f4(I; eliminate=4);
@test parent(first(gens(H))) == base_ring(H)
end

@testset "fglm" begin
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