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

HechtiDerLachs · 2025-05-14T10:19:26Z

It turns out that for the recursive ring interface tests one actually needs to implement divides. We should mention that in the documentation of the ring interface.

HechtiDerLachs · 2025-05-14T10:27:00Z

src/MPoly.jl

@@ -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]


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.

codecov · 2025-05-14T14:05:32Z

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.37%. Comparing base (7fcf80b) to head (f520650).
Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2077      +/-   ##
==========================================
- Coverage   88.39%   88.37%   -0.02%     
==========================================
  Files         125      126       +1     
  Lines       31578    31639      +61     
==========================================
+ Hits        27914    27962      +48     
- Misses       3664     3677      +13

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HechtiDerLachs · 2025-05-14T14:09:26Z

Any volunteers for approval? @thofma ? @lgoettgens ?

thofma · 2025-05-14T15:42:29Z

Hm, maybe @fingolfin and @lgoettgens can comment? They worked on the interface tests and probably know if this was intended.

fingolfin · 2025-05-15T11:15:08Z

docs/src/ring_interface.md

@@ -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)`. 


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...

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?

fingolfin · 2025-05-15T11:27:00Z

This was the backtrace leading to the problem (taking from Slack):

Basic functionality for commutative rings only: Error During Test at /home/matthias/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:232
  Got exception outside of a @test
  function divrem is not implemented for arguments
  MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}: -1
  MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}: -1
  
  Stacktrace:
    [1] divrem(a::MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}, b::MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}})
      @ AbstractAlgebra ~/.julia/packages/AbstractAlgebra/EAjNg/src/algorithms/GenericFunctions.jl:50
    [2] divrem(a::MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}, b::MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}})
      @ AbstractAlgebra ~/.julia/packages/AbstractAlgebra/EAjNg/src/AbstractAlgebra.jl:65
    [3] divides
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/src/algorithms/GenericFunctions.jl:156 [inlined]
    [4] divides_monagan_pearce(a::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}}, b::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}}, bits::Int64)
      @ AbstractAlgebra.Generic ~/.julia/packages/AbstractAlgebra/EAjNg/src/generic/MPoly.jl:2496
    [5] divides(a::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}}, b::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}})
      @ AbstractAlgebra.Generic ~/.julia/packages/AbstractAlgebra/EAjNg/src/generic/MPoly.jl:2555
    [6] #divexact#125
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/src/generic/MPoly.jl:2566 [inlined]
    [7] divexact
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/src/generic/MPoly.jl:2565 [inlined]
    [8] inv(x::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}})
      @ AbstractAlgebra ~/.julia/packages/AbstractAlgebra/EAjNg/src/Rings.jl:53
    [9] inv
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/src/AbstractAlgebra.jl:73 [inlined]
   [10] inv!
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/src/fundamental_interface.jl:337 [inlined]
   [11] test_mutating_op_like_neg(f::typeof(AbstractAlgebra.inv), f!::typeof(inv!), A::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}})
      @ TestExt ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Mutating-ops.jl:14
   [12] macro expansion
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:234 [inlined]
   [13] macro expansion
      @ ~/julia-1.11.1/share/julia/stdlib/v1.11/Test/src/Test.jl:1700 [inlined]
   [14] macro expansion
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:233 [inlined]
   [15] macro expansion
      @ ~/julia-1.11.1/share/julia/stdlib/v1.11/Test/src/Test.jl:1700 [inlined]
   [16] test_Ring_interface(R::AbstractAlgebra.Generic.MPolyRing{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}}; reps::Int64)
      @ TestExt ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:228
   [17] test_Ring_interface
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:222 [inlined]
   [18] macro expansion
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:521 [inlined]
   [19] macro expansion
      @ ~/julia-1.11.1/share/julia/stdlib/v1.11/Test/src/Test.jl:1700 [inlined]
   [20] test_MPoly_interface(Rxy::AbstractAlgebra.Generic.MPolyRing{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}}; reps::Int64)
      @ TestExt ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:521
   [21] test_MPoly_interface
      @ ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:512 [inlined]
   [22] test_Ring_interface_recursive(R::MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}; reps::Int64)
      @ TestExt ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:803
   [23] test_Ring_interface_recursive(R::MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}})
      @ TestExt ~/.julia/packages/AbstractAlgebra/EAjNg/ext/TestExt/Rings-conformance-tests.jl:798
   [24] top-level scope
      @ REPL[10]:1
   [25] eval
      @ ./boot.jl:430 [inlined]
   [26] eval_user_input(ast::Any, backend::REPL.REPLBackend, mod::Module)
      @ REPL ~/julia-1.11.1/share/julia/stdlib/v1.11/REPL/src/REPL.jl:245
   [27] repl_backend_loop(backend::REPL.REPLBackend, get_module::Function)
      @ REPL ~/julia-1.11.1/share/julia/stdlib/v1.11/REPL/src/REPL.jl:342
   [28] start_repl_backend(backend::REPL.REPLBackend, consumer::Any; get_module::Function)
      @ REPL ~/julia-1.11.1/share/julia/stdlib/v1.11/REPL/src/REPL.jl:327
   [29] run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool, backend::Any)
      @ REPL ~/julia-1.11.1/share/julia/stdlib/v1.11/REPL/src/REPL.jl:483
   [30] run_repl(repl::REPL.AbstractREPL, consumer::Any)
      @ REPL ~/julia-1.11.1/share/julia/stdlib/v1.11/REPL/src/REPL.jl:469
   [31] (::Base.var"#1139#1141"{Bool, Symbol, Bool})(REPL::Module)
      @ Base ./client.jl:446
   [32] #invokelatest#2
      @ ./essentials.jl:1055 [inlined]
   [33] invokelatest
      @ ./essentials.jl:1052 [inlined]
   [34] run_main_repl(interactive::Bool, quiet::Bool, banner::Symbol, history_file::Bool, color_set::Bool)
      @ Base ./client.jl:430
   [35] repl_main
      @ ./client.jl:567 [inlined]
   [36] _start()
      @ Base ./client.jl:541

fingolfin · 2025-05-15T11:39:38Z

So this started with test_Ring_interface_recursive(R::MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}})

As a recursive test was requested it then went to test mpoly rings over the given monoid algebra, i.e.:
test_MPoly_interface(Rxy::AbstractAlgebra.Generic.MPolyRing{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}}; reps::Int64)

which then calls test_Ring_interface on that mpoly ring, which ends up doing test_mutating_op_like_neg(f::typeof(AbstractAlgebra.inv), f!::typeof(inv!), A::AbstractAlgebra.Generic.MPoly{MonoidAlgebraElem{QQFieldElem, MonoidAlgebra{QQFieldElem, MPolyQuoRing{MPolyDecRingElem{QQFieldElem, QQMPolyRingElem}}}}})

And that test then ends up doing:

         @test isone(AbstractAlgebra.inv(one(R)))
         test_mutating_op_like_neg(AbstractAlgebra.inv, inv!, one(R))
         test_mutating_op_like_neg(AbstractAlgebra.inv, inv!, -one(R))

This eventually triggers a call to divides(a::MPoly{T}, b::MPoly{T}) where {T <: RingElement}

and so on.

So how to handle this. Some option:

teach the "generic" inv and/or divides methods for polynomial rings to better handle division by a constant polynomial, and there handle division by 1 or -1 (avoiding a call to inv and/or divides in the coefficient ring)
we just don't do this kind of test in the conformance test (not so nice as this has found bugs in the past)
we come up with a way to "gate" this test so that only rings that are declared as "supports division" are tested this way -> this is basically the same problem which stalled PR Add conformance tests for is_unit & is_nilpotent #1947

For 3 one possible way forward would be via the _implements trait from #1957 ...

fingolfin · 2025-05-15T11:44:08Z

All that said, I really don't want divides to be a required part of the ring interface.

thofma · 2025-05-15T16:26:38Z

Not clear what the "ring interface" promises. "If you implement these methods for your ring type, then the recursive tests will pass (modulo bugs in your code)"?

I am happy to try out 3). If this is not an option (because of time reasons), what about hiding the test behind a try ... catch e .... !(e isa NotImplementedError)?

This reverts commit 7f6d41f.

HechtiDerLachs · 2025-05-23T13:22:52Z

I updated this in view of #2096 . Now it does not contain changes to the docu anymore.

HechtiDerLachs added 2 commits May 14, 2025 12:18

Update the ring interface docu.

7f6d41f

Add type assertion for empty lists.

5759ae5

HechtiDerLachs commented May 14, 2025

View reviewed changes

fingolfin reviewed May 15, 2025

View reviewed changes

fingolfin mentioned this pull request May 21, 2025

Don't use inv and inv! in ring conformance tests #2096

Merged

Revert "Update the ring interface docu."

f520650

This reverts commit 7f6d41f.

HechtiDerLachs changed the title ~~Update the ring interface docu~~ ~~Update the ring interface docu~~ Fix generation of random polynomials May 23, 2025

lgoettgens changed the title ~~~~Update the ring interface docu~~ Fix generation of random polynomials~~ Improve type stability of ConformanceTests.generate_element(::MPolyRing) May 23, 2025

lgoettgens approved these changes May 23, 2025

View reviewed changes

lgoettgens enabled auto-merge (squash) May 23, 2025 13:22

lgoettgens changed the title ~~Improve type stability of ConformanceTests.generate_element(::MPolyRing)~~ Fix edge-case in ConformanceTests.generate_element(::MPolyRing) May 23, 2025

fingolfin approved these changes May 23, 2025

View reviewed changes

lgoettgens merged commit ba700e4 into Nemocas:master May 23, 2025
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Fix edge-case in `ConformanceTests.generate_element(::MPolyRing)` #2077

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