How to metapgrogram with custom-defined spins?

ITensor Julia Questions
1

Hi everyone!

I just started using ITensor.jl and was trying to define a custom group of sitetype e.g. Q-state Potts; what I was trying to do is as following:

  1. I define the general rules for the Hilbert space for all Q-state potts model, with Q as a hyper-parameter, and write it down as Make-a-Custom-Local-Hilbert-Space indicated
  2. I wrap it as a string and use common Julia meta-prog trick to parse it from a for loop e.g. Q in [2, 3, 4, …]

However, during the 2nd step I found it impossible to parse the script and interpolate Q correctly, it seems that strings like ::SiteType"Q={Q}" can’t be directly treated. May I ask if there’s any existing solutions to my need? Or any other workaround is welcome as well.

Thank you for any help or comment!

2

Thanks for the question. My recommendation would be to not do this using tricks with strings, but in one of the following ways below:

  1. one way would be to just define your space function to accept an optional dim keyword argument
function ITensors.space(::SiteType"Q"; dim=2)
 ...
end

then make your op overloads like this:

function op(on::OpName"Name", st::SiteType"Q", s::Index)
....
end

so that you have access to the actual site index s in your op function body, and you can get its dimension by just calling dim(s). Note that this version of op is expected to return an ITensor, not a matrix.

  1. use the pattern used for the “Qudit” site type, code here:
    https://github.com/ITensor/ITensors.jl/blob/main/src/physics/site_types/qudit.jl
    The main thing to notice is that calls to op are routed through the function labeled #interface at the end of the file. This passes additional d::Int dimension arguments to the op overloads earlier in the file, which return matrices.
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