Add \

[AlexRobson]

Closes #163

I had a look at this as I hit it leading to #163. There are some (lower/upper) triangular special cases in \ that are handled.

One exception is Diagonal. As right now it seems to lose it's nameddimness, which I didn't deal with:

Diagonal(NamedDimsArray{(:a, :b)}(rand(5, 5)))
5×5 Diagonal{Float64, Vector{Float64}}: # Not a NamedDim
UpperTriangular(NamedDimsArray{(:a, :b)}(rand(5, 5)))
5×5 UpperTriangular{Float64, NamedDimsArray{(:a, :b), Float64, 2, Matrix{Float64}}}: NamedDim

I terms of allocations:

A, r2, b = rand(5, 5), rand(5, 3), rand(5)
b_nda = NamedDimsArray{(:foo,)}(b)
A_nda = NamedDimsArray{(:foo, :bar)}(A)
@btime A \ b # 537.798 ns (3 allocations: 544 bytes
@btime A_nda \ b_nda # 561.098 ns (4 allocations: 560 bytes)

Atril = tril(A)
Atril_nda = NamedDimsArray{(:foo, :bar,)}(Atril)

@btime Atril \ b # 181.387 ns (1 allocation: 128 bytes)
@btime Atril_nda \ b_nda # 196.036 ns (2 allocations: 144 bytes)

and similar for the Triangular specialisations the one extra allocation.

[codecov]

Codecov Report

Merging #184 (f9874a9) into master (be6c28b) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #184      +/-   ##
==========================================
+ Coverage   95.40%   95.48%   +0.07%     
==========================================
  Files          13       13              
  Lines         588      598      +10     
==========================================
+ Hits          561      571      +10     
  Misses         27       27              

Impacted Files	Coverage Δ
src/functions_linearalgebra.jl	95.65% <100.00%> (+0.65%)	⬆️
src/name_operations.jl	100.00% <100.00%> (ø)

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