Add row/colsupport for InvLayout(TriangularLayout) properly (#341)

* Implement inv(TriangularLayout) properly

* Support ranges

Project.toml

@@ -1,6 +1,6 @@
 name = "LazyArrays"
 uuid = "5078a376-72f3-5289-bfd5-ec5146d43c02"
-version = "2.1.8"
+version = "2.1.9"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"

src/linalg/inv.jl

@@ -184,4 +184,23 @@ getindex(L::ApplyMatrix{<:Any,typeof(/)}, k::Integer, ::Colon) = permutedims(L.a
 getindex(L::ApplyMatrix{<:Any,typeof(/)}, k::Integer, j::Integer) = L[k,:][j]
 
 
-inv_layout(::LazyLayouts, _, A) = ApplyArray(inv, A)
+inv_layout(::LazyLayouts, _, A) = ApplyArray(inv, A)
+
+function colsupport(lay::AbstractInvLayout{TriLay}, A, j) where {S,TriLay<:TriangularLayout{S}}
+    isempty(j) && return 1:0
+    B, = arguments(lay, A)
+    if S == 'U'
+        return firstindex(B, 2):(maximum(j) - firstindex(B, 2) + 1)
+    else # S == 'L' 
+        return minimum(j):size(B, 2)
+    end 
+end 
+function rowsupport(lay::AbstractInvLayout{TriLay}, A, k) where {S,TriLay<:TriangularLayout{S}}
+    isempty(k) && return 1:0
+    B, = arguments(lay, A) 
+    if S == 'U' 
+        return minimum(k):size(B, 1) 
+    else # S == 'L'
+        return firstindex(B, 1):(maximum(k) - firstindex(B, 1) + 1)
+    end 
+end

test/bandedtests.jl

@@ -934,4 +934,21 @@ LinearAlgebra.lmul!(β::Number, A::PseudoBandedMatrix) = (lmul!(β, A.data); A)
     end
 end
 
+@testset "Issue #329" begin
+    # Make sure that we aren't giving the incorrect bandwidths 
+    U = UpperTriangular(ApplyArray(inv, brand(5, 5, 1, 2)))
+    invU = inv(U)
+    L = LowerTriangular(ApplyArray(inv, brand(10, 10, 3, 4)))
+    invL = inv(L)
+    @test colsupport(invU, 1) == 1:1 
+    @test colsupport(invU, 3) == 1:3 
+    @test rowsupport(invU, 1) == 1:5 
+    @test rowsupport(invU, 4) == 4:5 
+    @test rowsupport(invU, 5) == 5:5 
+    @test colsupport(invL, 1) == 1:10 
+    @test colsupport(invL, 5) == 5:10 
+    @test rowsupport(invL, 1) == 1:1 
+    @test rowsupport(invL, 4) == 1:4 
+end
+
 end # module

test/ldivtests.jl

@@ -181,4 +181,28 @@ end
     @test Z \ Y ≈ [-2.0 1.0; 1.5 -0.5]
 end
 
-end # module
+@testset "Issue #329" begin
+    U = UpperTriangular(ApplyArray(inv, rand(5, 5)))
+    invU = inv(U)
+    L = LowerTriangular(ApplyArray(inv, rand(10, 10)))
+    invL = inv(L)
+    @test colsupport(invU, 1) == 1:1 
+    @test colsupport(invU, 3) == 1:3
+    @test colsupport(invU, 1:3) == 1:3 
+    @test rowsupport(invU, 1) == 1:5 
+    @test rowsupport(invU, 4) == 4:5 
+    @test rowsupport(invU, 5) == 5:5 
+    @test rowsupport(invU, 3:5) == 3:5
+    @test colsupport(invL, 1) == 1:10 
+    @test colsupport(invL, 5) == 5:10 
+    @test colsupport(invL, 2:4) == 2:10
+    @test rowsupport(invL, 1) == 1:1 
+    @test rowsupport(invL, 4) == 1:4 
+    @test rowsupport(invL, 2:2:4) == 1:4
+    @test colsupport(invU, ()) == 1:0
+    @test rowsupport(invU, ()) == 1:0 
+    @test colsupport(invL, ()) == 1:0 
+    @test rowsupport(invL, ()) == 1:0
+end
+
+end # module