triangular rot180 (#257)

* copy for banded AdjOrTrans * Update test_tribanded.jl
JuliaLinearAlgebra · Oct 3, 2023 · 59f4758 · 59f4758
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diff --git a/src/tribanded.jl b/src/tribanded.jl
@@ -94,3 +94,9 @@ end
     LUT = uplo == 'U' ? LowerTriangular : UpperTriangular
     tbsv!(uploT, 'T', unit, size(A,1), bandwidth(A,bwdim), bandeddata(LUT(A')), x)
 end
+
+
+rot180(A::UpperTriangular{<:Any,<:AbstractBandedMatrix}) = LowerTriangular(rot180(parent(A)))
+rot180(A::UnitUpperTriangular{<:Any,<:AbstractBandedMatrix}) = UnitLowerTriangular(rot180(parent(A)))
+rot180(A::LowerTriangular{<:Any,<:AbstractBandedMatrix}) = UpperTriangular(rot180(parent(A)))
+rot180(A::UnitLowerTriangular{<:Any,<:AbstractBandedMatrix}) = UnitUpperTriangular(rot180(parent(A)))
diff --git a/test/test_tribanded.jl b/test/test_tribanded.jl
@@ -100,4 +100,16 @@ import BandedMatrices: BandedColumns, BandedRows
         @test L̃ \ B ≈ Matrix(L̃) \ B
         @test B / L̃ ≈ B / Matrix(L̃)
     end
+
+    @testset "rot180" begin
+        B = brand(5,5,2,1)
+        @test rot180(UpperTriangular(B)) isa LowerTriangular{<:Any,<:BandedMatrix}
+        @test rot180(UnitUpperTriangular(B)) isa UnitLowerTriangular{<:Any,<:BandedMatrix}
+        @test rot180(LowerTriangular(B)) isa UpperTriangular{<:Any,<:BandedMatrix}
+        @test rot180(UnitLowerTriangular(B)) isa UnitUpperTriangular{<:Any,<:BandedMatrix}
+        @test rot180(UpperTriangular(B)) == rot180(Matrix(UpperTriangular(B)))
+        @test rot180(UnitUpperTriangular(B)) == rot180(Matrix(UnitUpperTriangular(B)))
+        @test rot180(LowerTriangular(B)) == rot180(Matrix(LowerTriangular(B)))
+        @test rot180(UnitLowerTriangular(B)) == rot180(Matrix(UnitLowerTriangular(B)))
+    end
 end