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Fix edge-case in ConformanceTests.generate_element(::MPolyRing) #2077

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Merged
merged 3 commits into from
May 23, 2025
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Fix edge-case in ConformanceTests.generate_element(::MPolyRing) #2077

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7f6d41f
Update the ring interface docu.
HechtiDerLachs May 14, 2025
5759ae5
Add type assertion for empty lists.
HechtiDerLachs May 14, 2025
f520650
Revert "Update the ring interface docu."
HechtiDerLachs May 23, 2025
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2 changes: 2 additions & 0 deletions docs/src/ring_interface.md
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Expand Up @@ -505,6 +505,8 @@ throwing an exception, returning meaningless results, hanging or crashing. The
function should only be called with `check=false` if it is already known that the
division will be exact.

***Note:*** For the *recursive* ring tests to work, one needs to also implement `divides(f::MyElem, g::MyElem)`.
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I think divides is only required for euclidean rings: only test_EuclideanRing_interface calls it. Which is in turn only invoked automatically for univariate polynomial rings over a field...

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And there are generic divides methods for that, i.e.:

divides(f::PolyRingElem{T}, g::PolyRingElem{T}) where T <: RingElement
divides(z::PolyRingElem{T}, x::T) where T <: RingElement

So it would be really good to know what the actual problem you run into was?


### Inverse

```julia
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2 changes: 1 addition & 1 deletion src/MPoly.jl
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Expand Up @@ -1467,7 +1467,7 @@ function ConformanceTests.generate_element(Rx::MPolyRing)
len_bound = 8
exp_bound = rand(1:5)
len = rand(0:len_bound)
coeffs = [ConformanceTests.generate_element(R) for _ in 1:len]
coeffs = elem_type(R)[ConformanceTests.generate_element(R) for _ in 1:len]
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In case of empty lists, this was of type Vector{Any} despite the generation function being type stable. This caused more problems down the road.

exps = [[rand(0:exp_bound) for _ in 1:num_gens] for _ in 1:len]
return Rx(coeffs, exps)
end
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