From a6c87bcaee281cde3362769df3c7e829fa291821 Mon Sep 17 00:00:00 2001
From: Sheehan Olver <solver@mac.com>
Date: Mon, 15 Mar 2021 22:26:46 +0000
Subject: [PATCH 1/2] Suport SubTridiagonalLayout

---
 Project.toml         |  2 +-
 src/interfaceimpl.jl | 24 +++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index bd779e05..1b1a1258 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "BandedMatrices"
 uuid = "aae01518-5342-5314-be14-df237901396f"
-version = "0.16.8"
+version = "0.16.9"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
diff --git a/src/interfaceimpl.jl b/src/interfaceimpl.jl
index ce4f8a6b..5cb4309a 100644
--- a/src/interfaceimpl.jl
+++ b/src/interfaceimpl.jl
@@ -51,8 +51,30 @@ inbands_setindex!(J::SymTridiagonal, v, k::Integer, j::Integer) =
 isbanded(::Tridiagonal) = true
 bandwidths(::Tridiagonal) = (1,1)
 
+struct SubTridiagonalLayout <: AbstractBandedLayout end
+
 sublayout(::AbstractTridiagonalLayout, ::Type{<:Tuple{AbstractUnitRange{Int},AbstractUnitRange{Int}}}) =
-    BandedLayout()
+    SubTridiagonalLayout()
+
+function _BandedMatrix(::SubTridiagonalLayout, V::AbstractMatrix{T}) where T
+    A = parent(V)
+    kr,jr = parentindices(V)
+    m,n = size(V)
+    dat = Matrix{T}(undef, 3, n)
+
+    c,a,b = supdiagonaldata(A), diagonaldata(A), supdiagonaldata(A)
+    if first(jr) == 1
+        copyto!(view(dat, 1, 2:n), view(c, jr[2:end] .- 1))
+    else
+        copyto!(view(dat, 1, :), view(c, jr .- 1))
+    end
+    copyto!(view(dat, 2, :), view(a, jr))
+    copyto!(view(dat, 3, :), view(b, jr))
+    
+    sh = first(kr)-first(jr)
+    _BandedMatrix(dat, m, 1-sh, 1+sh)
+end
+    
 
 ###
 # rot180

From 8b0ae6cdeb215f7b2fe989f49a53bb9e9a91055b Mon Sep 17 00:00:00 2001
From: Sheehan Olver <solver@mac.com>
Date: Tue, 23 Mar 2021 08:32:04 +0000
Subject: [PATCH 2/2] Update interfaceimpl.jl

---
 src/interfaceimpl.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/interfaceimpl.jl b/src/interfaceimpl.jl
index 5cb4309a..e1e115c6 100644
--- a/src/interfaceimpl.jl
+++ b/src/interfaceimpl.jl
@@ -62,7 +62,7 @@ function _BandedMatrix(::SubTridiagonalLayout, V::AbstractMatrix{T}) where T
     m,n = size(V)
     dat = Matrix{T}(undef, 3, n)
 
-    c,a,b = supdiagonaldata(A), diagonaldata(A), supdiagonaldata(A)
+    c,a,b = subdiagonaldata(A), diagonaldata(A), supdiagonaldata(A)
     if first(jr) == 1
         copyto!(view(dat, 1, 2:n), view(c, jr[2:end] .- 1))
     else