`\(::UniformScaling, ::Diagonal{T,Array{T,1}})` returns dense `Matrix` when `T` is abstract #37359

StevenWhitaker · 2020-09-02T19:58:57Z

As stated in the title, \(::UniformScaling, ::Diagonal{T,Array{T,1}}) returns a dense Matrix when T is abstract. It seems that, ideally, a Diagonal matrix should be returned (as is the case when T is concrete). (This is for the case when T <: Number is true; I haven't looked at what happens when T <: Number is false.)

julia> versioninfo()
Julia Version 1.5.1
Commit 697e782ab8 (2020-08-25 20:08 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-9.0.1 (ORCJIT, skylake)
Environment:
  JULIA_NUM_THREADS = 8

julia> I \ Diagonal(ones(Integer, 4)) # T abstract --> returns Array
4×4 Array{Float64,2}:
 1.0  0.0
 0.0  1.0  0.0
 0.0  0.0  1.0  0.0
 0.0  0.0  1.0

julia> I \ Diagonal(ones(Int, 4)) # T concrete --> returns Diagonal
4×4 Diagonal{Float64,Array{Float64,1}}:
 1.0   ⋅    ⋅ 
  ⋅   1.0   ⋅    ⋅ 
  ⋅    ⋅   1.0   ⋅ 
  ⋅    ⋅   1.0

martinholters · 2020-09-03T09:11:06Z

Fix should be as simple as:

--- a/stdlib/LinearAlgebra/src/diagonal.jl
+++ b/stdlib/LinearAlgebra/src/diagonal.jl
@@ -174,6 +174,7 @@ end
 (*)(x::Number, D::Diagonal) = Diagonal(x * D.diag)
 (*)(D::Diagonal, x::Number) = Diagonal(D.diag * x)
 (/)(D::Diagonal, x::Number) = Diagonal(D.diag / x)
+(\)(x::Number, D::Diagonal) = Diagonal(x \ D.diag)
 
 function (*)(Da::Diagonal, Db::Diagonal)
     nDa, mDb = size(Da, 2), size(Db, 1)

If someone wants to try this out and make a PR out of it - go for it!

…t type and a subtype of Number JuliaLang#37359

dkarrasch · 2020-09-11T09:22:55Z

While @mbauman, maybe there is something else to be improved here.

martinholters added the good first issue label Sep 3, 2020

dkarrasch added the linear algebra label Sep 3, 2020

tantei3 added a commit to tantei3/julia that referenced this issue Sep 10, 2020

Fix: Return Diagonal Matrix for solve operator when matrix is abstrac…

55737c8

…t type and a subtype of Number JuliaLang#37359

tantei3 added a commit to tantei3/julia that referenced this issue Sep 10, 2020

Add test case for issue JuliaLang#37359

df847e3

tantei3 linked a pull request that will close this issue Sep 10, 2020

fix #37359 Return a Diagonal matrix when Abstract type is a Number #37504

Open

tantei3 added a commit to tantei3/julia that referenced this issue Sep 10, 2020

Added another test case for JuliaLang#37359

8636165

JuliaLang / julia

`\(::UniformScaling, ::Diagonal{T,Array{T,1}})` returns dense `Matrix` when `T` is abstract #37359

`\(::UniformScaling, ::Diagonal{T,Array{T,1}})` returns dense `Matrix` when `T` is abstract #37359

StevenWhitaker commented Sep 2, 2020

martinholters commented Sep 3, 2020 •

edited by fredrikekre

dkarrasch commented Sep 11, 2020

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`\(::UniformScaling, ::Diagonal{T,Array{T,1}})` returns dense `Matrix` when `T` is abstract #37359

`\(::UniformScaling, ::Diagonal{T,Array{T,1}})` returns dense `Matrix` when `T` is abstract #37359

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StevenWhitaker commented Sep 2, 2020

martinholters commented Sep 3, 2020 • edited by fredrikekre

dkarrasch commented Sep 11, 2020

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martinholters commented Sep 3, 2020 •

edited by fredrikekre