Add rrule for transpose (#319)

* add rrule for transpose

* add test rrule transpose

Author: lkdvos

ext/TensorKitChainRulesCoreExt/linalg.jl

@@ -69,6 +69,16 @@ function ChainRulesCore.rrule(
     return permute(tsrc, p; copy = true), permute_pullback
 end
 
+function ChainRulesCore.rrule(
+        ::typeof(transpose), tsrc::AbstractTensorMap, p::Index2Tuple; copy::Bool = false
+    )
+    function transpose_pullback(Δtdst)
+        invp = TensorKit._canonicalize(TupleTools.invperm(linearize(p)), tsrc)
+        return NoTangent(), transpose(unthunk(Δtdst), invp; copy = true), NoTangent()
+    end
+    return transpose(tsrc, p; copy = true), transpose_pullback
+end
+
 function ChainRulesCore.rrule(::typeof(tr), A::AbstractTensorMap)
     tr_pullback(Δtr) = NoTangent(), Δtr * id(domain(A))
     return tr(A), tr_pullback

test/autodiff/ad.jl

@@ -293,6 +293,7 @@ for V in spacelist
             C = randn(T, domain(A), codomain(A))
             test_rrule(*, A, C)
 
+            test_rrule(transpose, A, ((2, 5, 4), (1, 3)))
             symmetricbraiding && test_rrule(permute, A, ((1, 3, 2), (5, 4)))
             test_rrule(twist, A, 1)
             test_rrule(twist, A, [1, 3])