Fix indexing triangular matrices with undef elements in the parent (#…

…52530) I'm not totally sure about specializing`getindex` for numeric arrays, but this lets us display a triangular matrix where the parent is not initialized. ```julia julia> M = Matrix{BigFloat}(undef, 4, 4) 4×4 Matrix{BigFloat}: #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef #undef julia> UpperTriangular(M) 4×4 UpperTriangular{BigFloat, Matrix{BigFloat}}: #undef #undef #undef #undef ⋅ #undef #undef #undef ⋅ ⋅ #undef #undef ⋅ ⋅ ⋅ #undef ```
JuliaLang · Jan 26, 2024 · 1e45aba · 1e45aba
1 parent 4919dd7
commit 1e45aba
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Showing 2 changed files with 15 additions and 2 deletions.
diff --git a/stdlib/LinearAlgebra/src/triangular.jl b/stdlib/LinearAlgebra/src/triangular.jl
@@ -262,11 +262,11 @@ Base.isstored(A::UpperTriangular, i::Int, j::Int) =
 @propagate_inbounds getindex(A::UnitLowerTriangular{T}, i::Integer, j::Integer) where {T} =
     i > j ? A.data[i,j] : ifelse(i == j, oneunit(T), zero(T))
 @propagate_inbounds getindex(A::LowerTriangular, i::Integer, j::Integer) =
-    i >= j ? A.data[i,j] : zero(A.data[j,i])
+    i >= j ? A.data[i,j] : _zero(A.data,j,i)
 @propagate_inbounds getindex(A::UnitUpperTriangular{T}, i::Integer, j::Integer) where {T} =
     i < j ? A.data[i,j] : ifelse(i == j, oneunit(T), zero(T))
 @propagate_inbounds getindex(A::UpperTriangular, i::Integer, j::Integer) =
-    i <= j ? A.data[i,j] : zero(A.data[j,i])
+    i <= j ? A.data[i,j] : _zero(A.data,j,i)
 
 @propagate_inbounds function setindex!(A::UpperTriangular, x, i::Integer, j::Integer)
     if i > j

diff --git a/stdlib/LinearAlgebra/test/triangular.jl b/stdlib/LinearAlgebra/test/triangular.jl
@@ -811,6 +811,14 @@ end
     end
 end
 
+@testset "indexing partly initialized matrices" begin
+    M = Matrix{BigFloat}(undef, 2, 2)
+    U = UpperTriangular(M)
+    @test iszero(U[2,1])
+    L = LowerTriangular(M)
+    @test iszero(L[1,2])
+end
+
 @testset "special printing of Lower/UpperTriangular" begin
     @test occursin(r"3×3 (LinearAlgebra\.)?LowerTriangular{Int64, Matrix{Int64}}:\n 2  ⋅  ⋅\n 2  2  ⋅\n 2  2  2",
                    sprint(show, MIME"text/plain"(), LowerTriangular(2ones(Int64,3,3))))
@@ -820,6 +828,11 @@ end
                    sprint(show, MIME"text/plain"(), UpperTriangular(2ones(Int64,3,3))))
     @test occursin(r"3×3 (LinearAlgebra\.)?UnitUpperTriangular{Int64, Matrix{Int64}}:\n 1  2  2\n ⋅  1  2\n ⋅  ⋅  1",
                    sprint(show, MIME"text/plain"(), UnitUpperTriangular(2ones(Int64,3,3))))
+
+    # don't access non-structural elements while displaying
+    M = Matrix{BigFloat}(undef, 2, 2)
+    @test sprint(show, UpperTriangular(M)) == "BigFloat[#undef #undef; 0.0 #undef]"
+    @test sprint(show, LowerTriangular(M)) == "BigFloat[#undef 0.0; #undef #undef]"
 end
 
 @testset "adjoint/transpose triangular/vector multiplication" begin