From 7e58e3effaf0cc549ad5072df6ab87d4bd5e8969 Mon Sep 17 00:00:00 2001
From: Sheehan Olver <solver@mac.com>
Date: Wed, 26 Aug 2020 11:42:19 +0100
Subject: [PATCH] Fix + with degenerate bands

---
 Project.toml              |  2 +-
 src/generic/broadcast.jl  |  5 +++++
 test/test_broadcasting.jl | 13 ++++++++++++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index cfdeef84..249f915e 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "BandedMatrices"
 uuid = "aae01518-5342-5314-be14-df237901396f"
-version = "0.15.18"
+version = "0.15.19"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
diff --git a/src/generic/broadcast.jl b/src/generic/broadcast.jl
index a458dc6d..8cdcbace 100644
--- a/src/generic/broadcast.jl
+++ b/src/generic/broadcast.jl
@@ -641,6 +641,11 @@ function _banded_broadcast!(dest::AbstractMatrix, f, (A,B)::Tuple{AbstractMatrix
         # fill extra bands in dest
         fill!(view(data_d,1:d_u-max(A_u,B_u),:), z)
         fill!(view(data_d,d_u+max(A_l,B_l)+2:size(data_d,1),:), z)
+        # between A and B if non-overlapping
+        bs = max(-d_u,-B_l+1):min(A_u-1,d_l)
+        fill!(view(data_d, bs .+ d_u .+ 1, :), z)
+        bs = max(-d_u,-A_l+1):min(B_u-1,d_l)
+        fill!(view(data_d, bs .+ d_u .+ 1, :), z)
 
         # construct where B upper is zero
         # this is from band A_u:B_u+1
diff --git a/test/test_broadcasting.jl b/test/test_broadcasting.jl
index 890b4d17..b3332039 100644
--- a/test/test_broadcasting.jl
+++ b/test/test_broadcasting.jl
@@ -512,5 +512,16 @@ import BandedMatrices: BandedStyle, BandedRows
         
         @test copyto!(similar(bc, Float64), bc) == A .* B == B .* A == 
             BandedMatrix(B, (0,0)) == Matrix(A) .* B
-	end
+    end
+    
+    @testset "adding degenerate" begin
+        A = BandedMatrix(1 => 1:9)
+        B = BandedMatrix(-1 => 1:9)
+        C = BandedMatrix(Fill(-1,10,10),(1,1))
+        C .= A .+ B
+        @test diag(C) == Zeros{Int}(10)
+        C = BandedMatrix(Fill(-1,10,10),(1,1))
+        C .= A .+ B
+        @test diag(C) == Zeros{Int}(10)
+    end
 end
\ No newline at end of file