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fix: LQ pullback modifies input cotangents #226

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Merged
lkdvos merged 4 commits into from
May 11, 2026
Merged

fix: LQ pullback modifies input cotangents #226

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d131c1b
make sure LQ pullback does not modify input
lkdvos May 10, 2026
4e19011
remove unnecessary line
lkdvos May 10, 2026
742074c
copy of view to make sure this is copied
lkdvos May 11, 2026
b25c6c9
add tests for not modifying output tangents in chainrules
lkdvos May 11, 2026
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2 changes: 1 addition & 1 deletion src/pullbacks/lq.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -13,8 +13,8 @@ function check_and_prepare_lq_cotangents(
size(ΔQ) == size(Q) || throw(DimensionMismatch("ΔQ must have the same size as Q"))
ΔQ₁ .= view(ΔQ, 1:p, 1:n)
if p == minmn # full rank case, ΔQ₃ contains gauge-invariant information along Q₁
ΔQ₃ = copy(view(ΔQ, (minmn + 1):size(Q, 1), :)) # extra columns in the case of qr_full
Q₃ = view(Q, (minmn + 1):size(Q, 1), :)
ΔQ₃ = view(ΔQ, (minmn + 1):size(Q, 1), :)
ΔQ₃Q₁ᴴ = ΔQ₃ * Q₁'
mul!(ΔQ₃, ΔQ₃Q₁ᴴ, Q₁, -1, 1)
Δgauge_Q = norm(ΔQ₃, Inf)
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3 changes: 1 addition & 2 deletions src/pullbacks/qr.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,7 @@ function check_and_prepare_qr_cotangents(
size(ΔQ) == size(Q) || throw(DimensionMismatch("ΔQ must have the same size as Q"))
ΔQ₁ .= view(ΔQ, 1:m, 1:p)
if p == minmn # full rank case, ΔQ₃ contains gauge-invariant information along Q₁
ΔQ₃ = ΔQ[:, (minmn + 1):size(Q, 2)] # extra columns in the case of qr_full
Q₁ = view(Q, :, 1:minmn)
ΔQ₃ = copy(view(ΔQ, :, (minmn + 1):size(Q, 2))) # extra columns in the case of qr_full
Q₃ = view(Q, :, (minmn + 1):size(Q, 2))
Q₁ᴴΔQ₃ = Q₁' * ΔQ₃
mul!(ΔQ₃, Q₁, Q₁ᴴΔQ₃, -1, 1)
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