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Add characteristic for multivariate quotient rings over fields #4241

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Oct 24, 2024
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Add characteristic for multivariate quotient rings over fields #4241

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8 changes: 8 additions & 0 deletions src/Rings/MPolyQuo.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,14 @@ oscar_origin_ring(Q::MPolyQuoRing) = base_ring(Q)

default_ordering(Q::MPolyQuoRing) = default_ordering(base_ring(Q))

# Only for fields for now because of things like char(ZZ[x, y]/<2>) = 2
function characteristic(Q::MPolyQuoRing{<:MPolyRingElem{T}}) where {T <: FieldElement}
if is_zero(one(Q))
return 1
end
return characteristic(coefficient_ring(Q))
end

##############################################################################
#
# Quotient ring elements
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6 changes: 6 additions & 0 deletions test/Rings/MPolyQuo.jl
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Expand Up @@ -36,6 +36,12 @@

B,q = quo(R, x^3+y,y^2; ordering=lex(R))
@test A.I == B.I

@test characteristic(quo(R, ideal(x))[1]) == 0
@test characteristic(quo(R, ideal(R, 1))[1]) == 1

S, (s, t) = GF(5)[:s, :t]
@test characteristic(quo(S, ideal([s, t]))[1]) == 5
end

@testset "MpolyQuo.manipulation" begin
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