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Don't copy or retain C in the TensorOperations rrules when β = Zero() #555

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Merged
leburgel merged 3 commits into from
Sep 26, 2026
Merged

Don't copy or retain C in the TensorOperations rrules when β = Zero() #555

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905aeaf
Avoid copying and retaining `C` in TensorOperations rrules when `β = …
leburgel Sep 24, 2026
d82411f
Simplify
leburgel Sep 25, 2026
7c0e716
Merge branch 'main' into lb/zero-beta-rrules
leburgel Sep 25, 2026
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10 changes: 7 additions & 3 deletions ext/TensorKitChainRulesCoreExt/tensoroperations.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@ function ChainRulesCore.rrule(
α::Number, β::Number, ba...
)
C′ = tensoradd!(copy(C), A, pA, conjA, α, β, ba...)
# only keep `C` alive on the tape if `dβ` needs it
C_β = _needs_tangent(β) ? C : nothing

projectA = ProjectTo(A)
projectC = ProjectTo(C)
Expand Down Expand Up @@ -49,7 +51,7 @@ function ChainRulesCore.rrule(
else
ZeroTangent()
end
dβ = _needs_tangent(β) ? @thunk(projectβ(inner(C, ΔC))) : ZeroTangent()
dβ = _needs_tangent(β) ? @thunk(projectβ(inner(C_β, ΔC))) : NoTangent()
dba = map(_ -> NoTangent(), ba)
return NoTangent(), dC, dA, NoTangent(), NoTangent(), dα, dβ, dba...
end
Expand All @@ -66,6 +68,7 @@ function ChainRulesCore.rrule(
α::Number, β::Number, ba...
)
C′ = tensorcontract!(copy(C), A, pA, conjA, B, pB, conjB, pAB, α, β, ba...)
C_β = _needs_tangent(β) ? C : nothing

projectA = ProjectTo(A)
projectB = ProjectTo(B)
Expand Down Expand Up @@ -138,7 +141,7 @@ function ChainRulesCore.rrule(
else
ZeroTangent()
end
dβ = _needs_tangent(β) ? @thunk(projectβ(inner(C, ΔC))) : ZeroTangent()
dβ = _needs_tangent(β) ? @thunk(projectβ(inner(C_β, ΔC))) : NoTangent()
dba = map(_ -> NoTangent(), ba)
return NoTangent(), dC,
dA, NoTangent(), NoTangent(),
Expand All @@ -156,6 +159,7 @@ function ChainRulesCore.rrule(
α::Number, β::Number, ba...
)
C′ = tensortrace!(copy(C), A, p, q, conjA, α, β, ba...)
C_β = _needs_tangent(β) ? C : nothing

projectA = ProjectTo(A)
projectC = ProjectTo(C)
Expand Down Expand Up @@ -190,7 +194,7 @@ function ChainRulesCore.rrule(
else
ZeroTangent()
end
dβ = _needs_tangent(β) ? @thunk(projectβ(inner(C, ΔC))) : ZeroTangent()
dβ = _needs_tangent(β) ? @thunk(projectβ(inner(C_β, ΔC))) : NoTangent()
dba = map(_ -> NoTangent(), ba)
return NoTangent(), dC, dA, NoTangent(), NoTangent(), NoTangent(), dα, dβ, dba...
end
Expand Down
7 changes: 7 additions & 0 deletions test/chainrules/tensoroperations.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ using TensorKit
using TensorKit: type_repr, SectorDict
using TensorOperations
using ChainRulesCore
using VectorInterface: Zero
using ChainRulesTestUtils
using Random
using LinearAlgebra
Expand Down Expand Up @@ -47,6 +48,7 @@ for V in spacelist
for conjA in (false, true)
C = randn!(TensorOperations.tensoralloc_add(T, A, p, conjA, Val(false)))
test_rrule(tensortrace!, C, A, p, q, conjA, α, β; atol, rtol)
test_rrule(tensortrace!, C, A, p, q, conjA, α, Zero() ⊢ NoTangent(); atol, rtol)
end
end
end
Expand All @@ -65,6 +67,7 @@ for V in spacelist

C2 = randn!(TensorOperations.tensoralloc_add(T, A, p, true, Val(false)))
test_rrule(tensoradd!, C2, A, p, true, α, β; atol, rtol)
test_rrule(tensoradd!, C1, A, p, false, α, Zero() ⊢ NoTangent(); atol, rtol)

A = rand(Bool) ? C1 : C2
end
Expand Down Expand Up @@ -107,6 +110,10 @@ for V in spacelist
tensorcontract!, C, A, pA, conjA, B, pB, conjB, pAB, α, β;
atol, rtol
)
test_rrule(
tensorcontract!, C, A, pA, conjA, B, pB, conjB, pAB, α,
Zero() ⊢ NoTangent(); atol, rtol
)
end
end
end
Expand Down
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