Allow pushing to vector after 3-arg ldiv! (#43510)

Co-authored-by: Daniel Karrasch <[email protected]>

stdlib/LinearAlgebra/src/factorization.jl

@@ -114,16 +114,27 @@ end
 /(B::TransposeAbsVec, adjF::Adjoint{<:Any,<:Factorization}) = adjoint(adjF.parent \ adjoint(B))
 
 
-# support the same 3-arg idiom as in our other in-place A_*_B functions:
-function ldiv!(Y::AbstractVecOrMat, A::Factorization, B::AbstractVecOrMat)
+function ldiv!(Y::AbstractVector, A::Factorization, B::AbstractVector)
+ require_one_based_indexing(Y, B)
+ m, n = size(A, 1), size(A, 2)
+ if m > n
+ Bc = copy(B)
+ ldiv!(A, Bc)
+ return copyto!(Y, 1, Bc, 1, n)
+ else
+ return ldiv!(A, copyto!(Y, B))
+ end
+end
+function ldiv!(Y::AbstractMatrix, A::Factorization, B::AbstractMatrix)
  require_one_based_indexing(Y, B)
  m, n = size(A, 1), size(A, 2)
  if m > n
  Bc = copy(B)
  ldiv!(A, Bc)
  return copyto!(Y, view(Bc, 1:n, :))
  else
- return ldiv!(A, copyto!(Y, view(B, 1:m, :)))
+ copyto!(view(Y, 1:m, :), view(B, 1:m, :))
+ return ldiv!(A, Y)
  end
 end
 

stdlib/LinearAlgebra/test/lu.jl

@@ -426,4 +426,13 @@ end
  end
 end
 
+@testset "can push to vector after 3-arg ldiv! (#43507)" begin
+ u = rand(3)
+ A = rand(3,3)
+ b = rand(3)
+ ldiv!(u,lu(A),b)
+ push!(b,4.0)
+ @test length(b) == 4
+end
+
 end # module TestLU

stdlib/LinearAlgebra/test/qr.jl

@@ -270,11 +270,19 @@ end
  b = randn(3)
  b0 = copy(b)
  c = randn(2)
+ B = randn(3,3)
+ B0 = copy(B)
+ C = randn(2,3)
  @test A \b ≈ ldiv!(c, qr(A ), b)
  @test b == b0
+ @test A \B ≈ ldiv!(C, qr(A ), B)
+ @test B == B0
  c0 = copy(c)
+ C0 = copy(C)
  @test Ac\c ≈ ldiv!(b, qr(Ac, ColumnNorm()), c)
  @test c0 == c
+ @test Ac\C ≈ ldiv!(B, qr(Ac, ColumnNorm()), C)
+ @test C0 == C
 end
 
 @testset "Issue reflector of zero-length vector" begin