JuliaLang / julia / #37784

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Commit Message

Copy parent in copy_similar for Symmetric/Hermitian (#54473)

This should be equivalent to copying the `Symmetric`/`Hermitian` matrix,
as only one triangular half is used. However, this reduces latency when
the parent is a `Matrix` (and possibly others too, although I've not
checked this).

```julia
julia> using LinearAlgebra

julia> A = rand(2,2); H = Hermitian(A);

julia> @time eigen(H);
  0.342207 seconds (440.61 k allocations: 22.926 MiB, 99.95% compilation time) # nightly
  0.260913 seconds (326.62 k allocations: 16.926 MiB, 99.93% compilation time) # This PR
```
Copying the parent is also marginally faster, although this doesn't
really matter in `eigen`:
```julia
julia> A = rand(1000,1000); H = Hermitian(A);

julia> @btime LinearAlgebra.copy_similar($H, Float64);
  1.839 ms (3 allocations: 7.63 MiB) # nightly
  1.760 ms (3 allocations: 7.63 MiB) # This PR
```

---------

Co-authored-by: Daniel Karrasch <daniel.karrasch@posteo.de>

Run Details

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16 existing lines in 5 files now uncovered.

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