Restrict convert rrule to trivialtensormap

Jutho · Jun 28, 2024 · 76078de · 76078de
1 parent c15b7ab
commit 76078de
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Showing 2 changed files with 7 additions and 3 deletions.
diff --git a/ext/TensorKitChainRulesCoreExt/constructors.jl b/ext/TensorKitChainRulesCoreExt/constructors.jl
@@ -17,8 +17,10 @@ function ChainRulesCore.rrule(::typeof(Base.copy), t::AbstractTensorMap)
     return copy(t), copy_pullback
 end
 
+# this rule does not work for generic symmetries, as we currently have no way to
+# project back onto the symmetric subspace
 function ChainRulesCore.rrule(::typeof(Base.convert), T::Type{<:Array},
-                              t::AbstractTensorMap)
+                              t::TrivialTensorMap)
     A = convert(T, t)
     function convert_pullback(ΔA)
         ∂t = TensorMap(unthunk(ΔA), codomain(t), domain(t))

diff --git a/test/ad.jl b/test/ad.jl
@@ -143,8 +143,10 @@ Vlist = ((ℂ^2, (ℂ^3)', ℂ^3, ℂ^2, (ℂ^2)'),
         test_rrule(copy, T1)
         test_rrule(copy, T2)
 
-        test_rrule(convert, Array, T1)
-        test_rrule(TensorMap, convert(Array, T1), space(T1))
+        T1 isa TrivialTensorMap && test_rrule(convert, Array, T1)
+        T2 isa TrivialTensorMap && test_rrule(TensorMap, convert(Array, T1), space(T1))
+        # TODO: can we make these methods/tests work for generic symmetries?
+        # the main problem here is finitedifferencing generates non-symmetric entries
     end
 
     @timedtestset "Basic Linear Algebra with scalartype $T" for T in (Float64, ComplexF64)