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Add hermitianpart method for Number types #1445

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ab99211
Update README.md
GianmarcoCuppari Sep 18, 2025
fbf9475
Update README.md
GianmarcoCuppari Sep 18, 2025
a2358df
Merge remote-tracking branch 'upstream/master'
GianmarcoCuppari Oct 4, 2025
9335758
Add hermitianpart method for Number types
GianmarcoCuppari Sep 16, 2025
8bf4fdc
Apply suggestion to return Float64 for scalars; update docstring and …
GianmarcoCuppari Sep 16, 2025
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19 changes: 19 additions & 0 deletions README.md
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@@ -1,5 +1,24 @@
# LinearAlgebra

---
## 🚀 About this fork

This is my fork of LinearAlgebra.jl for contributing to Julia as part of my GSoC 2026 preparation.

**My contributions:**
- [PR #1445](https://github.com/JuliaLang/LinearAlgebra.jl/pull/1445) - Add hermitianpart method for Number types
- Active in issues: Coming

**Original repository:** [JuliaLang/LinearAlgebra.jl](https://github.com/JuliaLang/LinearAlgebra.jl)

---

# LinearAlgebra

This package is part of the Julia standard library (stdlib).

LinearAlgebra.jl provides functionality for performing linear algebra operations in Julia.

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Can you please remove all these changes?

This package is part of the Julia standard library (stdlib).

`LinearAlgebra.jl` provides functionality for performing linear algebra operations in Julia.
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9 changes: 8 additions & 1 deletion src/symmetric.jl
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Expand Up @@ -1003,19 +1003,26 @@ end

"""
hermitianpart(A::AbstractMatrix, uplo::Symbol=:U) -> Hermitian
hermitianpart(x::Number) -> Number

Return the Hermitian part of the square matrix `A`, defined as `(A + A') / 2`, as a
[`Hermitian`](@ref) matrix. For real matrices `A`, this is also known as the symmetric part
of `A`; it is also sometimes called the "operator real part". The optional argument `uplo` controls the corresponding argument of the
[`Hermitian`](@ref) view. For real matrices, the latter is equivalent to a
[`Symmetric`](@ref) view.

For scalar inputs `x`, the function returns the real part of `x`. Standard integer scalars
are promoted to `Float64` to align with the behavior of 1×1 Hermitian matrices, while other numeric types
(`Float32`, `BigInt`, `Rational`, `BigFloat`) are preserved.

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I'd suggest to leave this out, too.

See also [`hermitianpart!`](@ref) for the corresponding in-place operation.

!!! compat "Julia 1.10"
This function requires Julia 1.10 or later.
"""

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Suggested change

The docstring needs to be attached to the function definition, otherwise Julia doesn't know where it belongs.

hermitianpart(A::AbstractMatrix, uplo::Symbol=:U) = Hermitian(_hermitianpart(A), uplo)
hermitianpart(x::Number) = float(real(x))
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Suggested change
hermitianpart(x::Number) = float(real(x))
hermitianpart(x::Number) = real(x)

I believe this will get promoted if necessary by other mechanisms, so there is no need to enforce it per se.


"""
hermitianpart!(A::AbstractMatrix, uplo::Symbol=:U) -> Hermitian
Expand Down Expand Up @@ -1052,4 +1059,4 @@ function Base.replace_in_print_matrix(A::HermOrSym,i::Integer,j::Integer,s::Abst
ijminmax = minmax(i, j)
inds = A.uplo == 'U' ? ijminmax : reverse(ijminmax)
Base.replace_in_print_matrix(parent(A), inds..., s)
end
end
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Suggested change
end
end

It's common style to have an empty line at the end. No need to modify this.

10 changes: 10 additions & 0 deletions test/symmetric.jl
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Expand Up @@ -1035,6 +1035,16 @@ end
@test Aherm isa Hermitian
@test Aherm.uplo == LinearAlgebra.char_uplo(uplo)
end
@testset "hermitianpart for numbers" begin
@test hermitianpart(3 + 4im) == 3
@test hermitianpart(5) == 5.0
@test typeof(hermitianpart(5)) == Float64
@test hermitianpart(2.5) == 2.5
@test hermitianpart(-1 + 0im) == -1
@test typeof(hermitianpart(3 + 4im)) == 3.0
@test typeof(hermitianpart(3 + 4im)) == Float64
@test typeof(hermitianpart(2.5 + 3im)) == Float64
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Suggested change
@test typeof(hermitianpart(5)) == Float64
@test hermitianpart(2.5) == 2.5
@test hermitianpart(-1 + 0im) == -1
@test typeof(hermitianpart(3 + 4im)) == 3.0
@test typeof(hermitianpart(3 + 4im)) == Float64
@test typeof(hermitianpart(2.5 + 3im)) == Float64
@test hermitianpart(2.5) == 2.5
@test hermitianpart(-1 + 0im) == -1
@test typeof(hermitianpart(3 + 4im)) == 3.0

These type tests wouldn't be needed anymore.

end
end

@testset "Structured display" begin
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