initialize `ComplexSpace` from vector errors

[ogauthe]

I would like to write generic code that works for any sectortype and returns a space. I have an issue with the Trivial sector:

function make_space(s::Sector)
    return Vect[sectortype(s)]([s=>1])
end

make_space(U1Irrep(0))  # Rep[U₁](…) of dim 1:\n0 => 1
make_space(SU2Irrep(0))   # Rep[SU₂](…) of dim 1:\n0 => 1
make_space(Trivial())  # MethodError

I use this logic in QuantumKitHub/PEPSKit.jl#263

Is this expected behavior or should I submit a fix?

[borisdevos]

Hi Olivier!

This is expected behavior. If you check this line, it allows you to pass a vector of pairs as you do for the non-Trivial sectors.
However, for Vect[Trivial] = ComplexSpace, this line (or the constructor below) is what you want to call. Since for this sector type there's only one object Trivial(), there's no point in passing a vector since it can only have 1 element.

If your function make_space will always only take one object at a time, simply passing the pair will work. If not, you can make a dictionary, since this constructor exists for all sectors.

Hope this helps!

[lkdvos]

I think this really is a little bit of an oversight on our part, where GradedSpace allows generic iterables and ComplexSpace doesn't.
If this helps you, I would be happy to have that feature added for convenience/uniformity?
It might really just be as simple as just removing the ::Generator type restriction here:

TensorKit.jl/src/spaces/complexspace.jl

Line 33 in 155aa89

ComplexSpace(g::Base.Generator; kwargs...) = ComplexSpace(g...; kwargs...)

[ogauthe]

Thank you for the answers. Here I expect many sectors in the generic case, it just happens there is only 1 for Trivial. A better suited example would be

function make_space(v::Vector{<:Sector})
     return Vect[eltype(v)](v .=> 1)
end

make_space([SU2Irrep(0)])
make_space([U1Irrep(1), U1Irrep(2)])
make_space([Trivial()])

Thank you for the tip of using a dictionary, it fixes the issue.

I still think it would be great to have the same interface for GradedSpace and ComplexSpace and use the code above in a generic way - I did not even know these were different types.