Update ext/TensorKitCUDAExt/cutensormap.jl

Co-authored-by: Lukas Devos <[email protected]>

Author: kshyatt

ext/TensorKitCUDAExt/cutensormap.jl

@@ -153,10 +153,9 @@ end
 
 # Scalar implementation
 #-----------------------
-function TensorKit.scalar(t::CuTensorMap)
-    # TODO: should scalar only work if N₁ == N₂ == 0?
-    return @allowscalar dim(codomain(t)) == dim(domain(t)) == 1 ?
-        first(blocks(t))[2][1, 1] : throw(DimensionMismatch())
+function TensorKit.scalar(t::CuTensorMap{T, S, 0, 0}) where {T, S}
+    inds = findall(!iszero, t.data)
+    return isempty(inds) ? zero(scalartype(t)) : @allowscalar @inbounds t.data[only(inds)
 end
 
 function Base.convert(