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Add +/- for Number and AbstractMatrix to LinearAlgebra #29951

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Add +/- for Number and AbstractMatrix to LinearAlgebra #29951

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b277445
Add `+/-` for `Number` and `AbstractMatrix` to `LinearAlgebra`
dalum Nov 7, 2018
3e27085
Add tests
dalum Nov 7, 2018
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6 changes: 6 additions & 0 deletions stdlib/LinearAlgebra/src/uniformscaling.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,12 @@ isposdef(J::UniformScaling) = isposdef(J.λ)
(-)(J::UniformScaling, B::BitArray{2}) = J - Array(B)
(-)(A::AbstractMatrix, J::UniformScaling) = A + (-J)

# Promotion of scalar to uniform scaling under addition/subtraction
(+)(a::Number, A::AbstractMatrix) = UniformScaling(a) + A
(+)(A::AbstractMatrix, a::Number) = A + UniformScaling(a)
(-)(a::Number, A::AbstractMatrix) = UniformScaling(a) - A
(-)(A::AbstractMatrix, a::Number) = A - UniformScaling(a)
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I wonder if this could/should be done via the promotion mechanism. Interestingly, that would address the behavior of scaling a matrix by a scalar as well.


# Unit{Lower/Upper}Triangular matrices become {Lower/Upper}Triangular under
# addition with a UniformScaling
for (t1, t2) in ((:UnitUpperTriangular, :UpperTriangular),
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10 changes: 10 additions & 0 deletions stdlib/LinearAlgebra/test/uniformscaling.jl
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Expand Up @@ -64,6 +64,16 @@ end
@test UniformScaling(α)/α == UniformScaling(1.0)
end

@testset "conversion of Number" begin
α = randn()
J = UniformScaling(α)
A = randn(2, 2)
@test α + A == J + A
@test A + α == A + J
@test α - A == J - A
@test A - α == A - J
end

@testset "det and logdet" begin
@test det(I) === true
@test det(1.0I) === 1.0
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