JuliaLang / JuliaLang/LinearAlgebra.jl
ldiv! with transpose uses less allocations than ldiv!
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Description
ldiv! with transposed LU factors uses less allocations and ldiv! with the original LU factors. For example,
julia> VERSION
v"1.2.0-DEV.487"
julia> using LinearAlgebra, BenchmarkTools
julia> A = rand(3,3); b = rand(3); x = rand(3); F = lu(A);
julia> @btime ldiv!($x, $F, $b);
169.591 ns (3 allocations: 160 bytes)
julia> @btime ldiv!($x, transpose($F), $b);
103.688 ns (0 allocations: 0 bytes)
Is this expected behavior?
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the two ldiv! benchmarks from the issue with Julia, LinearAlgebra, and BenchmarkTools, then compare the allocation behavior of the original and transposed LU-factor paths. Done means establishing whether the allocation difference is expected and, if not, identifying the relevant implementation or test location for a fix.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- julia
- Domain
- performance
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100