Add fallback for +(::BlockDiagonal,::Diagonal) when blocks are not square

Project.toml

@@ -1,7 +1,7 @@
 name = "BlockDiagonals"
 uuid = "0a1fb500-61f7-11e9-3c65-f5ef3456f9f0"
 authors = ["Invenia Technical Computing Corporation"]
-version = "0.1.37"
+version = "0.1.38"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/base_maths.jl

@@ -42,8 +42,11 @@ function Base.:+(B::BlockDiagonal, M::StridedMatrix)
     return A
 end
 
-function Base.:+(B::BlockDiagonal, M::Diagonal)::BlockDiagonal
+function Base.:+(B::BlockDiagonal, M::Diagonal)
     size(B) == size(M) || throw(DimensionMismatch("dimensions must match"))
+    if !all(is_square, blocks(B))
+        return Matrix(B) + M # Fallback on the generic Base method
+    end
     A = copy(B)
     d = diag(M)
     row = 1

test/base_maths.jl

@@ -19,6 +19,8 @@ using Test
     b64 = BlockDiagonal([rand(rng, 2, 2), rand(rng, 2, 2)])
     b32 = BlockDiagonal([rand(rng, Float32, 2, 2), rand(rng, Float32, 2, 2)])
 
+    bns = BlockDiagonal([rand(rng, N1, N2), rand(rng, N2, N3), rand(rng, N3, N1)])
+
     @testset "Addition" begin
         @testset "BlockDiagonal + BlockDiagonal" begin
             @test b1 + b1 isa BlockDiagonal
@@ -58,6 +60,15 @@ using Test
             @test D + b1 isa BlockDiagonal
             @test D + b1 == D + Matrix(b1)
             @test_throws DimensionMismatch D′ + b1
+
+            # Non-square blocks
+            @test D + bns isa Matrix
+            @test D + bns == D + Matrix(bns)
+            @test_throws DimensionMismatch D′ + bns
+
+            @test bns + D isa Matrix
+            @test bns + D == D + Matrix(bns)
+            @test_throws DimensionMismatch bns + D′
         end
 
         @testset "BlockDiagonal + UniformScaling" begin
@@ -69,11 +80,11 @@ using Test
             @test 5I + b1 == 5I + Matrix(b1)
         end
     end  # Addition
-    
+
     @testset "Subtraction" begin
         @test -b1 isa BlockDiagonal
         @test b1 - b1 isa BlockDiagonal
-        
+
         @test -b1 == -Matrix(b1)
         @test b1 - b1 == Matrix(b1) - Matrix(b1)
         @test Matrix(b1) - b2 == Matrix(b1) - Matrix(b2)