Specialize isbanded for OneElement (#333)

JuliaArrays · Jul 21, 2024 · a7ddcca · a7ddcca
1 parent 1896e30
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diff --git a/src/oneelement.jl b/src/oneelement.jl
@@ -360,6 +360,11 @@ end
 adjoint(A::OneElementMatrix) = OneElement(adjoint(A.val), reverse(A.ind), reverse(A.axes))
 transpose(A::OneElementMatrix) = OneElement(transpose(A.val), reverse(A.ind), reverse(A.axes))
 
+# isbanded
+function LinearAlgebra.isbanded(A::OneElementMatrix, kl::Integer, ku::Integer)
+    iszero(getindex_value(A)) || kl <= A.ind[2] - A.ind[1] <= ku
+end
+
 # tril/triu
 
 function tril(A::OneElementMatrix, k::Integer=0)

diff --git a/test/runtests.jl b/test/runtests.jl
@@ -2501,6 +2501,37 @@ end
         @test A / (2 + 3.0im) === OneElement(val / (2 + 3.0im), (2,2), (3,4)) == B / (2 + 3.0im)
     end
 
+
+    @testset "isbanded" begin
+        A = OneElement(3, (2,3), (4,5))
+        @test !isdiag(A)
+        @test istriu(A)
+        @test !istril(A)
+        @test LinearAlgebra.isbanded(A, 1, 2)
+        @test LinearAlgebra.isbanded(A, -1, 2)
+        @test !LinearAlgebra.isbanded(A, 2, 2)
+
+        A = OneElement(3, (4,2), (4,5))
+        @test !isdiag(A)
+        @test !istriu(A)
+        @test istril(A)
+        @test LinearAlgebra.isbanded(A, -2, -2)
+        @test LinearAlgebra.isbanded(A, -2, 2)
+        @test !LinearAlgebra.isbanded(A, 2, 2)
+
+        for A in (OneElement(3, (2,2), (4,5)), OneElement(3, (1,1), (1,2)), OneElement(3, (8,7), (2,1)))
+            @test isdiag(A)
+            @test istriu(A)
+            @test istril(A)
+        end
+
+        for A in (OneElement(0, (2,3), (4,5)), OneElement(0, (3,2), (4,5)))
+            @test isdiag(A)
+            @test istriu(A)
+            @test istril(A)
+        end
+    end
+
     @testset "zero/iszero" begin
         v = OneElement(10, 3, 4)
         @test v + zero(v) == v