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LinearAlgebra: use instead of == for tr tests in symmetric.jl #55143

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merged 1 commit into from
Jul 17, 2024

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After investigating #54090, I found that the issue was not caused by the effects of checksquare, but by the use of the @simd macro within tr(::Matrix):

function tr(A::Matrix{T}) where T
n = checksquare(A)
t = zero(T)
@inbounds @simd for i in 1:n
t += A[i,i]
end
t
end

While simply removing the @simd macro was considered, the strict left-to-right summation without @simd otherwise is not necessarily more accurate, so I concluded that the problem lies in the test code, which tests the (strict) equality of two different tr execution results. I have modified the test code to use instead of ==.

@aviatesk aviatesk added backport 1.10 Change should be backported to the 1.10 release backport 1.11 Change should be backported to release-1.11 labels Jul 16, 2024
@aviatesk aviatesk changed the title LinearAlgebra: use LinearAlgebra: use instead of == for tr tests in symmetric.jl Jul 16, 2024
…c.jl

After investigating #54090, I found that the issue was
not caused by the effects of `checksquare`, but by the use of the
`@simd` macro within `tr(::Matrix)`:
https://github.com/JuliaLang/julia/blob/0945b9d7740855c82a09fed42fbf6bc561e02c77/stdlib/LinearAlgebra/src/dense.jl#L373-L380

While simply removing the `@simd` macro was considered, the strict
left-to-right summation without `@simd` otherwise is not necessarily
more accurate, so I concluded that the problem lies in the test code,
which tests the (strict) equality of two different `tr` execution
results. I have modified the test code to use `≈` instead of `==`.

- fixes #54090
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@dkarrasch dkarrasch left a comment

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Yes, testing for equality only makes sense when you implicitly assume that the exact same code path is taken (and perhaps more).

@dkarrasch dkarrasch added the linear algebra Linear algebra label Jul 17, 2024
@aviatesk aviatesk merged commit 7c9a465 into master Jul 17, 2024
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@aviatesk aviatesk deleted the avi/54090 branch July 17, 2024 08:39
aviatesk added a commit that referenced this pull request Jul 17, 2024
…#55143)

After investigating #54090, I found that the issue was
not caused by the effects of `checksquare`, but by the use of the
`@simd` macro within `tr(::Matrix)`:

https://github.com/JuliaLang/julia/blob/0945b9d7740855c82a09fed42fbf6bc561e02c77/stdlib/LinearAlgebra/src/dense.jl#L373-L380

While simply removing the `@simd` macro was considered, the strict
left-to-right summation without `@simd` otherwise is not necessarily
more accurate, so I concluded that the problem lies in the test code,
which tests the (strict) equality of two different `tr` execution
results. I have modified the test code to use `≈` instead of `==`.

- fixes #54090
aviatesk added a commit that referenced this pull request Jul 17, 2024
…#55143)

After investigating #54090, I found that the issue was
not caused by the effects of `checksquare`, but by the use of the
`@simd` macro within `tr(::Matrix)`:

https://github.com/JuliaLang/julia/blob/0945b9d7740855c82a09fed42fbf6bc561e02c77/stdlib/LinearAlgebra/src/dense.jl#L373-L380

While simply removing the `@simd` macro was considered, the strict
left-to-right summation without `@simd` otherwise is not necessarily
more accurate, so I concluded that the problem lies in the test code,
which tests the (strict) equality of two different `tr` execution
results. I have modified the test code to use `≈` instead of `==`.

- fixes #54090
@aviatesk aviatesk removed backport 1.10 Change should be backported to the 1.10 release backport 1.11 Change should be backported to release-1.11 labels Jul 17, 2024
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LinearAlgebra: unstable return value, affected by lazy string & @show in error path
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