`matmul` outcome changed between Julia 1.7 and 1.8-beta1

[rikhuijzer]

In ArrayLayouts.jl, there is a test comparing their implementation of muladd to base muladd:

julia> rng = StableRNG(1);

julia> X = randn(rng, ComplexF64, 8, 4);

julia> Y = randn(rng, 8, 2);
        
julia> @test all(mul(Y',X) .=== Y'X)

This test fails on Julia 1.8-beta1 and passes on earlier versions. I've narrowed it down to a change in outcome of Y'X:

Julia 1.7.2

julia> (Y'X)[1]
-1.3154858319870038 - 0.8411677016058232im

Julia 1.8-beta1

julia> (Y'X)[1]
-1.315485831987004 - 0.8411677016058232im

Is this change in outcome expected?

EDIT: This is probably related to JuliaLang/julia#44529.

[KristofferC]

I think this is JuliaLang/julia#43435. It is using BLAS now instead of a generic Julia method. Small differences are expected.

[rikhuijzer]

I think this is JuliaLang/julia#43435. It is using BLAS now instead of a generic Julia method. Small differences are expected.

Okay thank you, Kristoffer 🙂 I‘ll close this