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Fix truncrank when kept rank is larger than input rank #368

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Merged
lkdvos merged 2 commits into from
Feb 8, 2026
Merged

Fix truncrank when kept rank is larger than input rank #368

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e4aa683
Short-circuit truncrank to notrunc when kept rank is larger than input
Yue-Zhengyuan Feb 8, 2026
9f4a339
Consider strategy.rev
Yue-Zhengyuan Feb 8, 2026
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3 changes: 2 additions & 1 deletion src/factorizations/truncation.jl
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Expand Up @@ -171,7 +171,8 @@ function MAK.findtruncated(values::SectorVector, strategy::TruncationByOrder)

# dimensions are all 1 so no need to account for weight
if FusionStyle(I) isa UniqueFusion
perm = partialsortperm(parent(values), 1:strategy.howmany; strategy.by, strategy.rev)
howmany = min(length(parent(values)), strategy.howmany)
perm = partialsortperm(parent(values), 1:howmany; strategy.by, strategy.rev)
result = similar(values, Bool)
fill!(parent(result), false)
parent(result)[perm] .= true
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8 changes: 8 additions & 0 deletions test/tensors/factorizations.jl
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Expand Up @@ -254,6 +254,14 @@ for V in spacelist
@test isisometric(U)
@test isisometric(Vᴴ; side = :right)

# when rank of t is already smaller than truncrank
t_rank = ceil(Int, min(dim(codomain(t)), dim(domain(t))))
U, S, Vᴴ, ϵ = @constinferred svd_trunc(t; trunc = truncrank(t_rank + 1))
@test U * S * Vᴴ ≈ t
@test ϵ ≈ 0
@test isisometric(U)
@test isisometric(Vᴴ; side = :right)

# dimension of S is a float for IsingBimodule
nvals = round(Int, dim(domain(S)) / 2)
trunc = truncrank(nvals)
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