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Faster computation of injective resolutions #5497

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Faster computation of injective resolutions #5497

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6c89726
compute shorter irreducible resolution
annahofer00 Oct 1, 2025
1deb6f5
make injective_resolution faster
annahofer00 Oct 24, 2025
a8103fe
Merge branch 'oscar-system:master' into master
annahofer00 Oct 24, 2025
6878fa5
undo last commit
annahofer00 Oct 24, 2025
510e33e
Update experimental/InjectiveResolutions/src/InjectiveResolutions.jl
annahofer00 Oct 24, 2025
f5e4ffd
resolve failing tests
annahofer00 Nov 10, 2025
58df793
Merge branch 'master' of https://github.com/annahofer00/Oscar.jl
annahofer00 Nov 10, 2025
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15 changes: 7 additions & 8 deletions experimental/InjectiveResolutions/src/InjectiveResolutions.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -713,9 +713,9 @@ function _get_irreducible_ideal(kQ::MonoidAlgebra, J::IndecInj)
end

@doc raw"""
irreducible_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int = 0)
irreducible_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int = -1)

Return an irreducible resolution of $M$.
Return an irreducible resolution of $M$ (up to cohomological degree i).

!!! note
The monoid algebra $k[Q]$ must be normal.
Expand Down Expand Up @@ -759,7 +759,7 @@ by graded submodule of kQ^1 with 3 generators
over monoid algebra over rational field with cone of dimension 2
```
"""
function irreducible_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int=0)
function irreducible_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int=-1)
kQ = base_ring(M)
@req is_normal(kQ) "monoid algebra must be normal"

Expand Down Expand Up @@ -812,7 +812,7 @@ function irreducible_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int=0)
push!(cochain_maps, hi)

# end at cohomological degree i
if i > 0 && j == i
if j == i + 1
break
end
j = j + 1
Expand Down Expand Up @@ -955,7 +955,7 @@ function injective_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int)
#compute irreducible resolution of shifted module
a_shift = compute_shift(M, i+1)
M_a = twist(M, -G(a_shift))
irr_res = irreducible_resolution(M_a)
irr_res = irreducible_resolution(M_a,i)

#get injective modules up to cohomological degree i, i.e. J^0, J^1, ...,J^i
inj_modules = Vector{InjMod}()
Expand All @@ -968,7 +968,7 @@ function injective_resolution(M::SubquoModule{<:MonoidAlgebraElem}, i::Int)

#get all needed maps (as k-matrix or k[Q]-matrix?)
cochain_maps = [
matrix(irr_res.cochain_maps[k]) for k in eachindex(irr_res.cochain_maps) if 1 < k <= i+1
matrix(irr_res.cochain_maps[k]) for k in eachindex(irr_res.cochain_maps) if 1 <= k <= i+1
]
return InjRes(M, inj_modules, cochain_maps, length(inj_modules)-1, irr_res, a_shift)
end
Expand Down Expand Up @@ -1064,5 +1064,4 @@ export zeroth_local_cohomology

export MonoidAlgebra
export MonoidAlgebraIdeal
export MonoidAlgebraElem

export MonoidAlgebraElem
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