implement bandwidths for OneElement (#447)

* implement bandwidths for OneElement

* make improvements

* fix sparse(::SparseMatrixCSC)

* fix bandwidths for SparseMatrixCSC, add for SparseVector

* add bandwidths(::Zeros) behaviour for empty sparse structures

* add unit tests

* cleanup bandwidths

* Update interfaceimpl.jl

---------

Co-authored-by: Sheehan Olver <[email protected]>

Author: max-vassili3v

ext/BandedMatricesSparseArraysExt.jl

@@ -2,37 +2,53 @@ module BandedMatricesSparseArraysExt
 
 using BandedMatrices
 using BandedMatrices: _banded_rowval, _banded_colval, _banded_nzval
-using SparseArrays
+using SparseArrays, FillArrays
 import SparseArrays: sparse
 
 function sparse(B::BandedMatrix)
 	sparse(_banded_rowval(B), _banded_colval(B), _banded_nzval(B), size(B)...)
 end
 
 function BandedMatrices.bandwidths(A::SparseMatrixCSC)
-    l,u = -size(A,1),-size(A,2)
-
-    m,n = size(A)
+    l = u = -max(size(A,1),size(A,2))
+    n = size(A)[2]
     rows = rowvals(A)
     vals = nonzeros(A)
+
+    if isempty(vals)
+        return bandwidths(Zeros(1))
+    end
+
     for j = 1:n
         for ind in nzrange(A, j)
             i = rows[ind]
             # We skip non-structural zeros when computing the
             # bandwidths.
             iszero(vals[ind]) && continue
-            ij = abs(i-j)
-            if i ≥ j
-                l = max(l, ij)
-                u = max(u, -ij)
-            elseif i < j
-                l = max(l, -ij)
-                u = max(u, ij)
-            end
+            u = max(u, j-i)
+            l = max(l, i-j)
         end
     end
 
     l,u
 end
 
+#Treat as n x 1 matrix
+function BandedMatrices.bandwidths(A::SparseVector)
+    l = u = -size(A,1)
+    rows = rowvals(A)
+
+    if isempty(rows)
+        return bandwidths(Zeros(1))
+    end
+
+    for i in rows
+        iszero(i) && continue
+        u = max(u, 1-i)
+        l = max(l, i-1)
+    end
+    
+    l,u
+end
+
 end

src/BandedMatrices.jl

@@ -34,7 +34,7 @@ import ArrayLayouts: AbstractTridiagonalLayout, BidiagonalLayout, BlasMatLdivVec
                      symmetricuplo, transposelayout, triangulardata, triangularlayout, zero!,
                      QRPackedQLayout, AdjQRPackedQLayout
 
-import FillArrays: AbstractFill, getindex_value, _broadcasted_zeros, unique_value, OneElement, RectDiagonal
+import FillArrays: AbstractFill, getindex_value, _broadcasted_zeros, unique_value, OneElement, RectDiagonal, OneElementMatrix, OneElementVector
 
 const libblas = LinearAlgebra.BLAS.libblas
 const liblapack = LinearAlgebra.BLAS.liblapack

src/interfaceimpl.jl

@@ -56,6 +56,27 @@ bandwidths(::Tridiagonal) = (1,1)
 sublayout(::AbstractTridiagonalLayout, ::Type{<:Tuple{AbstractUnitRange{Int},AbstractUnitRange{Int}}}) =
     BandedLayout()
 
+#Implement bandwidths for OneElement structure
+function bandwidths(o::OneElementVector)
+    k = FillArrays.nzind(o)[1] # index of non-zero
+    n = length(o)
+    if k > n || k < 1
+        bandwidths(Zeros(o))
+    else
+        (k-1, 1-k)
+    end
+end
+
+function bandwidths(o::OneElementMatrix)
+    n,m = size(o)
+    k,j = Tuple(FillArrays.nzind(o))  # indices of non-zero entries
+    if k > n || j > m || k < 1 || j < 1
+        bandwidths(Zeros(o))
+    else
+        (k-j,j-k)
+    end
+end
+
 ###
 # rot180
 ###

test/test_interface.jl

@@ -1,10 +1,10 @@
 module TestInterface
 
-using BandedMatrices, LinearAlgebra, ArrayLayouts, FillArrays, Test
+using BandedMatrices, LinearAlgebra, ArrayLayouts, FillArrays, Test, Random
 import BandedMatrices: isbanded, AbstractBandedLayout, BandedStyle,
                         BandedColumns, bandeddata
 import ArrayLayouts: OnesLayout, UnknownLayout
-using InfiniteArrays
+using InfiniteArrays, SparseArrays
 
 struct PseudoBandedMatrix{T} <: AbstractMatrix{T}
     data::Array{T}
@@ -310,6 +310,18 @@ end
     @test layout_getindex(T,1:10,1:10) isa BandedMatrix
 end
 
+@testset "OneElement" begin
+    o = OneElement(1, 3, 5)
+    @test bandwidths(o) == (2,-2)
+    n,m = rand(1:10,2)
+    o = OneElement(1, (rand(1:n),rand(1:m)), (n, m))
+    @test bandwidths(o) == bandwidths(sparse(o))
+    o = OneElement(1, (n+1,m+1), (n, m))
+    @test bandwidths(o) == bandwidths(Zeros(o))
+    o = OneElement(1, 6, 5)
+    @test bandwidths(o) == bandwidths(Zeros(o))
+end
+
 @testset "rot180" begin
     A = brand(5,5,1,2)
     R = rot180(A)

test/test_miscs.jl

@@ -50,8 +50,17 @@ import BandedMatrices: _BandedMatrix, DefaultBandedMatrix
             @test bA isa BandedMatrix
             @test bA == A
             @test bandwidths(bA) == min.((l,u),9)
+            v = sparsevec(brand(10, 1, l, u))
+            @test bandwidths(v) == (l, min(0, u))
         end
 
+        l, u = -1, 0
+        A = brand(10, 10, l, u)
+        sA = sparse(A)
+        @test bandwidths(sA) == bandwidths(Zeros(1))
+        v = sparsevec(brand(10, 1, l, u))
+        @test bandwidths(v) == bandwidths(Zeros(1))
+
         for diags = [(-1 => ones(Int, 5),),
                      (-2 => ones(Int, 5),),
                      (2 => ones(Int, 5),),