"Inplace" iterators over the coefficients, monomials, terms and exponent vectors of a multivariate polynomial by joschmitt · Pull Request #2196 · Nemocas/AbstractAlgebra.jl

joschmitt · 2025-10-24T13:42:28Z

Add an inplace option to the iterators of exponents, coefficients, terms and monomials of a multivariate polynomial.
This is still a draft. Is this the "interface" we want?
Regarding the new functions coeff!, term! and exponent_vector!: Should they be exported (I did it for now because monomial! is exported as well)? Do I need to implement an "abstract fall-back" in src/MPoly.jl?

Nemocas/Nemo.jl#2161 implements the (few) necessary functions for QQMPolyRingElem. Using those, I get the following timings in oscar-system/Oscar.jl#5483 :

# Previously
julia> @btime inv_c[n-k+1:n];
  3.628 s (28973402 allocations: 1.73 GiB)

# With inplace iterators
julia> @btime inv_c[n-k+1:n];
  1.356 s (2811 allocations: 279.24 KiB)

So that moves in the right direction.

joschmitt · 2025-10-24T13:47:58Z

+   if !isassigned(m.coeffs, 1) || !is_one(m.coeffs[1])
+     m.coeffs[1] = one(base_ring(x))
+   end


This is a bit ugly, but it gets the monomials iterator to constant allocations. Otherwise it would allocate a new 1 all the time. Is this too much of a corner case?

Seems fine to me

codecov · 2025-10-29T14:16:18Z

Codecov Report

❌ Patch coverage is 90.90909% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.99%. Comparing base (995a497) to head (d62e1c5).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/MPoly.jl	55.55%	8 Missing ⚠️

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joschmitt · 2025-10-29T16:04:18Z

+# S may be the type of anything that can store an exponent vector, for example
+# Vector{Int}, ZZMatrix, ...
+struct MPolyExponentVectors{T <: AbstractAlgebra.RingElem, S}
   poly::T
+   inplace::Bool
+   temp::S # only used if inplace == true
+end


The exponent_vectors iterator can now in principle take anything as type for the exponents, as long as there is a exponent_vector!(::T, ...) method for that type. Now one can do exponent_vectors(Vector{ZZRingElem}, ::QQMPolyRingElem) and it would for example allow to add a variant exponent_vectors(ZZMatrix, ...) in Nemo like mentioned in oscar-system/Oscar.jl#5483 (comment) .

fingolfin · 2025-11-03T14:16:28Z

Thank you very much for working on this. It seems fine to me. But I'd like triage to have a look at it before merging.

lgoettgens · 2025-11-05T11:21:53Z

IMO this should also have the abstract fallbacks, see Nemocas/Nemo.jl#2161 (comment)

joschmitt · 2025-11-05T14:37:27Z

IMO this should also have the abstract fallbacks, see Nemocas/Nemo.jl#2161 (comment)

Also done.

lgoettgens

some more minor comments. I didn't really think about exponent vectors yet, mostly about the iterators that return some ring elem of some kind

lgoettgens · 2025-11-05T15:33:48Z

-function coefficients(a::MPolyRingElem{T}) where T <: RingElement
-   return Generic.MPolyCoeffs(a)
+function coefficients(a::MPolyRingElem{T}; inplace::Bool = false) where T <: RingElement
+   return Generic.MPolyCoeffs(a, inplace=inplace)


Suggested change

return Generic.MPolyCoeffs(a, inplace=inplace)

return Generic.MPolyCoeffs(a; inplace)

IMO a bit neater, but I don't really care

I never really got the hang of this syntax, so if you don't care, I'll prefer my version.

lgoettgens

Looks great! Thanks for working on this!

joschmitt · 2025-11-10T16:14:31Z

+
+If `inplace` is `true`, the elements of the iterator may share their memory. This
+means that an element returned by the iterator may be overwritten 'in place' in
+the next iteration step. This may result in significantly fewer memory allocations.


I added these sentences to the doc strings. I'm happy for any suggestions. If I understand the suggestion in oscar-system/Oscar.jl#5530 (comment) correctly, we want to have something to add to all iterator doc strings that allow inplace. So maybe we should agree on a nice wording here and then we can copy and paste it everywhere :)

@fingolfin @mjrodgers

EDIT: I kept this intentionally vague ("may") because with this generic code it might be that the inplace version actually doesn't do anything different (because something is not implemented for a particular type).

I like this, if others agree I will add this same wording to the other methods in Oscar.

Maybe mention that it might to lead to unexpected behavior when calling collect on such an iterator.

I added a bit more, so this is ready for the next round of feedback :)

I feel like in an ideal world, we would put this paragraph somewhere "central" in the documentation and just link there from all iterators that support inplace = true. But I don't know where.

Looks good to me, thanks. (And I agree, one "central place" would be great, but for the time being this here is fine.)

joschmitt · 2025-11-14T09:05:41Z

I'll merge this beginning of next week, if there are no further comments.

Use `@inferred` correctly and fix return type

joschmitt mentioned this pull request Oct 24, 2025

Towards inplace iterators for exponents of multivariate polynomials etc. Nemocas/Nemo.jl#2161

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joschmitt commented Oct 24, 2025

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joschmitt force-pushed the js/inplace branch 2 times, most recently from 4f33ce7 to 7275f84 Compare October 29, 2025 13:40

joschmitt mentioned this pull request Oct 29, 2025

Don't use AbstractAlgebra internals oscar-system/Oscar.jl#5508

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joschmitt force-pushed the js/inplace branch from 2bc128b to e577691 Compare October 29, 2025 15:20

joschmitt commented Oct 29, 2025

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joschmitt marked this pull request as ready for review October 29, 2025 16:04

joschmitt closed this Oct 30, 2025

joschmitt reopened this Oct 30, 2025

fingolfin added the triage label Nov 3, 2025

joschmitt changed the title ~~Towards inplace iterators for exponents of multivariate polynomials etc.~~ "Inplace" iterators over the coefficients, monomials, terms and exponent vectors of a multivariate polynomial Nov 4, 2025

joschmitt added the release notes: use title For PRs: the title of this PR is suitable for direct use in the release notes label Nov 4, 2025

fingolfin reviewed Nov 5, 2025

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Comment thread src/MPoly.jl Outdated

fingolfin reviewed Nov 5, 2025

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Comment thread src/MPoly.jl Outdated

joschmitt force-pushed the js/inplace branch from 85224a4 to 18cde7d Compare November 5, 2025 14:35

lgoettgens reviewed Nov 5, 2025

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lgoettgens approved these changes Nov 6, 2025

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joschmitt added 8 commits November 10, 2025 17:10

Towards inplace iterators for exponents of multivariate polynomials etc.

ff7c58d

Add one-element constructors

c4ef7ca

Fix type signature

13bc030

Allow "arbitrary" types for exponent vectors

7ebd24f

Add a small test

9100d4f

Make it Nemo proof

8bd71ef

Only allocate when asked

c774ba0

Provide "abstract" fallbacks

49c5192

joschmitt added 5 commits November 10, 2025 17:10

Re-add the "default" constructor

3057fdc

Do it differently

4a0ae6d

Remove some constructors

7d73418

Increase the odds

ef3b593

Add some documentation

d6e24a0

joschmitt force-pushed the js/inplace branch from a597880 to d6e24a0 Compare November 10, 2025 16:10

joschmitt commented Nov 10, 2025

View reviewed changes

fingolfin removed the triage label Nov 12, 2025

Add more documentation

d62e1c5

lgoettgens merged commit 0a6e99f into Nemocas:master Nov 17, 2025
23 checks passed

joschmitt deleted the js/inplace branch November 17, 2025 09:40

joschmitt added a commit to joschmitt/AbstractAlgebra.jl that referenced this pull request Nov 20, 2025

Fixup Nemocas#2196

a5c3bba

Use `@inferred` correctly and fix return type

This was referenced Nov 20, 2025

Fixup #2196 #2221

Merged

More inplace functions for the flint mpoly types Nemocas/Nemo.jl#2178

Merged

joschmitt added a commit to joschmitt/AbstractAlgebra.jl that referenced this pull request Nov 24, 2025

Fixup Nemocas#2196

102ec7b

Use `@inferred` correctly and fix return type

lgoettgens mentioned this pull request Mar 24, 2026

"Inplace" iterators over the coefficients, monomials, terms and exponent words of a free associative algebra element #2380

Merged

	return Generic.MPolyCoeffs(a, inplace=inplace)
	return Generic.MPolyCoeffs(a; inplace)

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joschmitt commented Nov 14, 2025

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