Fix Thin QR

Author: dlfivefifty

src/blockskylineqr.jl

@@ -97,7 +97,11 @@ end
 for Typ in (:StridedVector, :StridedMatrix, :AbstractVector, :AbstractMatrix)
     @eval function ldiv!(A::QR{<:Any,<:BlockSkylineMatrix}, B::$Typ)
         lmul!(adjoint(A.Q), B)
-        apply!(\, UpperTriangular(A.factors), B)
+        M,N = nblocks(A.factors)
+        MN = min(M,N)
+        V = view(A.factors,Block.(1:MN), Block.(1:MN))
+        apply!(\, UpperTriangular(V), view(B,1:size(V,1),:))
+        B
     end
 end
 

test/test_blockskylineqr.jl

@@ -39,8 +39,10 @@ using BlockBandedMatrices, LinearAlgebra, MatrixFactorizations
         b = randn(size(A,1))
         @test Q'b ≈ Q̃'b
         @test Q*b ≈ Q̃*b
+
+        @test Q'b ≈ lmul!(Q', copy(b)) ≈ Q̃'*b
 
-        @test_broken F\b ≈ ldiv!(F, copy(b))[1:15] ≈ Matrix(A)\b ≈ A\b
+        @test F\b ≈ ldiv!(F, copy(b))[1:15] ≈ Matrix(A)\b ≈ A\b
     end
 
     @testset "Wide QR" begin
@@ -60,8 +62,8 @@ using BlockBandedMatrices, LinearAlgebra, MatrixFactorizations
         b = randn(size(A,1))
         @test Q'b ≈ Q̃'b
         @test Q*b ≈ Q̃*b
-
-        @test_throws DimensionMismatch ldiv!(F, copy(b))
+        Q'b
+        # @test_broken DimensionMismatch ldiv!(F, copy(b))
 
         @test_broken F\b ≈ ldiv!(F, copy(b)) ≈ Matrix(A)\b ≈ A\b
     end