This surprised me: julia> typeof(copy(rand(4,4)')) Matrix{Float64} (alias for Array{Float64, 2}) julia> typeof(deepcopy(rand(4,4)')) LinearAlgebra.Adjoint{Float64, Matrix{Float64}} I have an algorithm which looks prettier when written assuming row-major order. To ensure the code looks pretty and …

The interface of copy is mostly a convention, but generally if the argument is a wrapper that provides a “view” (eg Adjoint, PermutedDimsArray, SubArray), would you expect that it copies the parent and makes a similar view? This may be a reasonable use case in some contexts, but that’s not how it w…

More generally, why is copy not preserving the type of the object it is copying?

copy was chosen as the function that materializes lazy adjoints and transposes (xref https://github.com/JuliaLang/julia/pull/25364 ).

But that was apparently when collect was supposed to be deprecated (replaced with Array), which didn’t happen… See https://github.com/JuliaLang/julia/issues/16029 In any case, I wonder what was the rationale: it seems more useful and intuitive to use collect or Array for materialization and have co…

This may be related to another thread of mine where I reported that adjointness ‘disappears’ after abs.: How to write generic low-rank updates?

I think that the fundamental question is why you would want to copy a LinearAlgebra.Adjoint.

That question seems weird to me, as it can be asked of any functionality. Here is of the top of my head: First and foremost, the whole point of LinearAlgebra.Adjoint is that it is lazy-ish, which permits certain optimizations. Otherwise we would just always use an explicit transpose. It is also th…

Yeah, I did expect it would copy the parent and make a similar view. I see how this can go wrong if the parent is much bigger. The status quo now makes sense to me (the current convention about copies of views). It is certainly not an intuitive convention to me, but I can hardly claim some universa…

As mentioned in the thread linked above julia> copy([1,2]') 1×2 LinearAlgebra.Adjoint{Int64,Array{Int64,1}}: 1 2 so copy does preserve Adjoint wrappers at times.

That final case is important — and hopefully proves the rule by exception — because adjoint vectors behave differently than one-row matrices.

Why is `copy(adjoint)` not an adjoint object?

Internals & Design

rafael.guerra February 16, 2021, 9:30am 3

Same remark seems to have been made here by @dlfivefifty. It does not say if a PR was created.

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Why is `copy(adjoint)` not an adjoint object?

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