From fa9a5dc799ba2d39068da0f03156180c9ce98a88 Mon Sep 17 00:00:00 2001
From: Sheehan Olver <solver@mac.com>
Date: Thu, 19 Dec 2024 16:14:44 +0000
Subject: [PATCH] Add one and UniformScaling constructor

---
 Project.toml               |  2 +-
 src/BandedMatrices.jl      |  2 +-
 src/banded/BandedMatrix.jl | 23 +++++++++++++++++++++++
 test/test_banded.jl        | 18 ++++++++++++++++++
 4 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index d04b17a3..e353618c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "BandedMatrices"
 uuid = "aae01518-5342-5314-be14-df237901396f"
-version = "1.8.0"
+version = "1.9.0"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
diff --git a/src/BandedMatrices.jl b/src/BandedMatrices.jl
index 4070958e..36959ba6 100644
--- a/src/BandedMatrices.jl
+++ b/src/BandedMatrices.jl
@@ -7,7 +7,7 @@ import Base: axes, axes1, getproperty, getindex, setindex!, *, +, -, ==, <, <=,
                >=, /, \, adjoint, transpose, showerror, convert, size, view,
                unsafe_indices, first, last, size, length, unsafe_length, step, to_indices,
                to_index, show, fill!, similar, copy, promote_rule, real, imag,
-               copyto!, Array, sum, sum!
+               copyto!, Array, sum, sum!, one
 
 using Base.Broadcast: AbstractArrayStyle, DefaultArrayStyle, Broadcasted
 import Base.Broadcast: BroadcastStyle, broadcasted
diff --git a/src/banded/BandedMatrix.jl b/src/banded/BandedMatrix.jl
index 26f2ffc8..4fa7f2f1 100644
--- a/src/banded/BandedMatrix.jl
+++ b/src/banded/BandedMatrix.jl
@@ -74,6 +74,20 @@ BandedMatrix{T}(::UndefInitializer, nm::NTuple{2,OneTo{Int}}, ab::NTuple{2,Integ
 BandedMatrix{V}(M::BandedMatrix) where {V} = _BandedMatrix(AbstractMatrix{V}(M.data), M.raxis, M.l, M.u)
 BandedMatrix(M::BandedMatrix{V}) where {V} = _BandedMatrix(AbstractMatrix{V}(M.data), M.raxis, M.l, M.u)
 
+function BandedMatrix{T, C, Ax}(A::UniformScaling, nm::NTuple{2,Integer}, (l,u)::NTuple{2,Integer}=(0,0)) where {T,C,Ax}
+    ret = BandedMatrix{T, C, Ax}(undef, nm, (l,u))
+    zero!(ret.data)
+    ret.data[u+1,:] .= A.λ
+    ret
+end
+BandedMatrix{T,C}(A::UniformScaling, nm::NTuple{2,Integer}, ab::NTuple{2,Integer}=(0,0)) where {T,C} = 
+    BandedMatrix{T, C, OneTo{Int}}(A, nm, ab)
+BandedMatrix{T}(A::UniformScaling, nm::NTuple{2,Integer}, ab::NTuple{2,Integer}=(0,0)) where T = 
+    BandedMatrix{T, Matrix{T}}(A, nm, ab)
+BandedMatrix(A::UniformScaling, nm::NTuple{2,Integer}, ab::NTuple{2,Integer}=(0,0)) = 
+    BandedMatrix{eltype(A)}(A, nm, ab)
+
+
 convert(::Type{BandedMatrix{V}}, M::BandedMatrix{V}) where {V} = M
 convert(::Type{BandedMatrix{V}}, M::BandedMatrix) where {V} =
         _BandedMatrix(convert(AbstractMatrix{V}, M.data), M.raxis, M.l, M.u)
@@ -1008,3 +1022,12 @@ function resize(A::BandedSubBandedMatrix, n::Integer, m::Integer)
     _BandedMatrix(reshape(resize!(vec(copy(bandeddata(A))), (l+u+1)*m), l+u+1, m), n, l,u)
 end
 
+###
+# one
+###
+
+function one(A::BandedMatrix)
+    m,n = size(A)
+    m==n || throw(DimensionMismatch("multiplicative identity defined only for square matrices"))
+    typeof(A)(I, (m,n))
+end
\ No newline at end of file
diff --git a/test/test_banded.jl b/test/test_banded.jl
index 390ceb76..b718ad36 100644
--- a/test/test_banded.jl
+++ b/test/test_banded.jl
@@ -568,6 +568,24 @@ include("mymatrix.jl")
         @test resize(view(A,2:3,2:5),5,5) isa BandedMatrix
         @test resize(view(A,2:3,2:5),5,5)[1:2,1:4] == A[2:3,2:5]
     end
+
+    @testset "UniformScaling" begin
+        @test BandedMatrix(I, (3,4)) == BandedMatrix{Int}(I, (3,4)) == BandedMatrix{Int,Matrix{Int}}(I, (3,4))  == BandedMatrix{Int,Matrix{Int},Base.OneTo{Int}}(I, (3,4)) == Matrix(I,(3,4))
+        @test eltype(BandedMatrix(I, (3,4))) == Bool
+        @test eltype(BandedMatrix{Int}(I, (3,4))) == Int
+        @test bandwidths(BandedMatrix(I, (3,4))) == (0,0)
+        @test bandwidths(BandedMatrix(I, (3,4), (1,2))) == (1,2)
+        @test_throws BoundsError BandedMatrix(I, (3,4), (-1,2))
+    end
+
+
+    @testset "one" begin
+        @test_throws DimensionMismatch one(brand(4,5,1,1))
+        Q = one(brand(5,5,1,1))
+        @test bandwidths(Q) == (0,0)
+        @test Q == I(5)
+        @test eltype(Q) == Float64
+    end
 end
 
 end # module