transpose specialization for DiagonalTensorMap (#335)

* add `transpose` specialization for `DiagonalTensorMap`

* add test

* slight test fixes

Author: lkdvos

src/tensors/diagonal.jl

@@ -211,7 +211,29 @@ function permute(
         end
         return d′
     else
-        throw(ArgumentError("invalid permutation $((p₁, p₂)) for tensor in space $(space(d))"))
+        throw(ArgumentError(lazy"invalid permutation $((p₁, p₂)) for tensor in space $(space(d))"))
+    end
+end
+
+function LinearAlgebra.transpose(
+        d::DiagonalTensorMap, (p₁, p₂)::Index2Tuple{1, 1}; copy::Bool = false
+    )
+    if p₁ === (1,) && p₂ === (2,)
+        return copy ? Base.copy(d) : d
+    elseif p₁ === (2,) && p₂ === (1,) # transpose
+        if has_shared_permute(d, (p₁, p₂)) # tranpose for bosonic sectors
+            return DiagonalTensorMap(copy ? Base.copy(d.data) : d.data, dual(d.domain))
+        end
+        d′ = typeof(d)(undef, dual(d.domain))
+        for (c, b) in blocks(d)
+            f = only(fusiontrees(codomain(d), c))
+            ((f′, _), coeff) = only(transpose(f, f, p₁, p₂))
+            c′ = f′.coupled
+            scale!(block(d′, c′), b, coeff)
+        end
+        return d′
+    else
+        throw(ArgumentError(lazy"invalid transposition $((p₁, p₂)) for tensor in space $(space(d))"))
     end
 end
 

test/tensors/diagonal.jl

@@ -119,19 +119,26 @@ diagspacelist = (
     if BraidingStyle(I) isa SymmetricBraiding
         @timedtestset "Permutations" begin
             t = DiagonalTensorMap(randn(ComplexF64, reduceddim(V)), V)
+            t_tm = convert(TensorMap, t)
+
+            # preserving diagonal
             t1 = @constinferred permute(t, $(((2,), (1,))))
-            if BraidingStyle(sectortype(V)) isa Bosonic
-                @test t1 ≈ transpose(t)
-            end
-            @test convert(TensorMap, t1) == permute(convert(TensorMap, t), (((2,), (1,))))
+            @test t1 isa DiagonalTensorMap
+            @test convert(TensorMap, t1) == permute(t_tm, (((2,), (1,))))
+            t1′ = @constinferred transpose(t)
+            @test t1′ isa DiagonalTensorMap
+            @test convert(TensorMap, t1′) == transpose(t_tm)
+            BraidingStyle(I) isa Bosonic && @test t1 ≈ t1′
+
+            # not preserving diagonal
             t2 = @constinferred permute(t, $(((1, 2), ())))
-            @test convert(TensorMap, t2) == permute(convert(TensorMap, t), (((1, 2), ())))
+            @test convert(TensorMap, t2) == permute(t_tm, (((1, 2), ())))
             t3 = @constinferred permute(t, $(((2, 1), ())))
-            @test convert(TensorMap, t3) == permute(convert(TensorMap, t), (((2, 1), ())))
+            @test convert(TensorMap, t3) == permute(t_tm, (((2, 1), ())))
             t4 = @constinferred permute(t, $(((), (1, 2))))
-            @test convert(TensorMap, t4) == permute(convert(TensorMap, t), (((), (1, 2))))
+            @test convert(TensorMap, t4) == permute(t_tm, (((), (1, 2))))
             t5 = @constinferred permute(t, $(((), (2, 1))))
-            @test convert(TensorMap, t5) == permute(convert(TensorMap, t), (((), (2, 1))))
+            @test convert(TensorMap, t5) == permute(t_tm, (((), (2, 1))))
         end
     end
     @timedtestset "Trace, Multiplication and inverse" begin