Char uplo in Bidiagonal constructor

[jishnub]

This is an internal constructor, but many methods involving Bidiagonal matrices currently use the Char uplo directly to construct a new Bidiagonal matrix. We therefore may require the constructors to accept a Char as well, wherever they accept a Symbol. This already works for some of the Bidiagonal constructors, and this PR plugs a missing case.

Fixes issues like

julia> B = Bidiagonal(fill(SMatrix{2,3}(1:6), 4), fill(SMatrix{1,3}(1:3), 3), :L)
4×4 Bidiagonal{StaticArraysCore.SArray{S, Int64, 2} where S<:Tuple, Vector{StaticArraysCore.SArray{S, Int64, 2} where S<:Tuple}}:
 [1 3 5; 2 4 6]        ⋅               ⋅               ⋅       
 [1 2 3]         [1 3 5; 2 4 6]        ⋅               ⋅       
       ⋅         [1 2 3]         [1 3 5; 2 4 6]        ⋅       
       ⋅               ⋅         [1 2 3]         [1 3 5; 2 4 6]

julia> 2B
ERROR: MethodError: no method matching Bidiagonal(::Vector{SMatrix{2, 3, Int64, 6}}, ::Vector{SMatrix{1, 3, Int64, 3}}, ::Char)
The type `Bidiagonal` exists, but no method is defined for this combination of argument types when trying to construct it.

Closest candidates are:
  Bidiagonal(::Vector{T}, ::Vector{S}, ::Symbol) where {T, S}
   @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra_2.jl/src/bidiag.jl:77
  Bidiagonal(::V, ::V, ::AbstractChar) where {T, V<:AbstractVector{T}}
   @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra_2.jl/src/bidiag.jl:71
  Bidiagonal(::V, ::V, ::Symbol) where {T, V<:AbstractVector{T}}
   @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra_2.jl/src/bidiag.jl:68
  ...

After this,

julia> 2B
4×4 Bidiagonal{StaticArraysCore.SArray{S, Int64, 2} where S<:Tuple, Vector{StaticArraysCore.SArray{S, Int64, 2} where S<:Tuple}}:
 [2 6 10; 4 8 12]        ⋅                 ⋅                 ⋅       
 [2 4 6]           [2 6 10; 4 8 12]        ⋅                 ⋅       
       ⋅           [2 4 6]           [2 6 10; 4 8 12]        ⋅       
       ⋅                 ⋅           [2 4 6]           [2 6 10; 4 8 12]

We may require that each method passes a Symbol as uplo, but this would be a much larger change, and the current approach seems to be less disruptive.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.74%. Comparing base (f0e36ea) to head (ed1b085).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1342      +/-   ##
==========================================
- Coverage   93.74%   93.74%   -0.01%     
==========================================
  Files          34       34              
  Lines       15769    15767       -2     
==========================================
- Hits        14783    14781       -2     
  Misses        986      986              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.