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Reuse du2 of Tridiagonal matrix for pivoting in lu! if extant #47564

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Merged
merged 4 commits into from
Nov 28, 2022
Merged

Reuse du2 of Tridiagonal matrix for pivoting in lu! if extant #47564

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a6e122d
Reuse `du2` of `Tridiagonal` matrix for pivoting in `lu!` if it alrea…
brenhinkeller Nov 14, 2022
0fc0bd1
Omit type check on `A.du2` since already guaranteed by type of `A`
brenhinkeller Nov 14, 2022
c10614d
Fix whitespace
brenhinkeller Nov 16, 2022
e65393c
Ensure `du2` is always initialized with zeros
brenhinkeller Nov 22, 2022
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11 changes: 9 additions & 2 deletions stdlib/LinearAlgebra/src/lu.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -527,7 +527,14 @@ function lu!(A::Tridiagonal{T,V}, pivot::Union{RowMaximum,NoPivot} = RowMaximum(
if dl === du
throw(ArgumentError("off-diagonals of `A` must not alias"))
end
du2 = fill!(similar(d, max(0, n-2)), 0)::V
# Check if Tridiagonal matrix already has du2 for pivoting
has_du2_defined = isdefined(A, :du2) && length(A.du2) == max(0, n-2)
if has_du2_defined
du2 = A.du2::V
else
du2 = similar(d, max(0, n-2))::V
end
fill!(du2, 0)

@inbounds begin
for i = 1:n
Expand Down Expand Up @@ -582,7 +589,7 @@ function lu!(A::Tridiagonal{T,V}, pivot::Union{RowMaximum,NoPivot} = RowMaximum(
end
end
end
B = Tridiagonal{T,V}(dl, d, du, du2)
B = has_du2_defined ? A : Tridiagonal{T,V}(dl, d, du, du2)
check && checknonsingular(info, pivot)
return LU{T,Tridiagonal{T,V},typeof(ipiv)}(B, ipiv, convert(BlasInt, info))
end
Expand Down