Matt Fishman

> Yes, so the main other things left for this PR in my mind were: > > * try implementing it using sum or `+` as you had mentioned previously...

Support for this will also be added to ITensorMPS.jl with this PR: https://github.com/ITensor/ITensorMPS.jl/pull/17.

> For the krylovdim I don't have too strong an opinion. Maybe the best thing is to think about what krylovdim of 0 or 1 means. So in your convention...

> Great. I think I like just plain "expand" also for the reason you said. Hopefully it is clear from doc strings and arguments what exactly it does in case...

@b-kloss https://github.com/ITensor/ITensors.jl/pull/929 is merged and registered in ITensors 0.3.16 so you can remove the `nullspace` implementation from this PR and set the `compat` entry of ITensors to 0.3.16 here: https://github.com/ITensor/ITensorTDVP.jl/blob/867a15a8e73cd4d889c7b8a9113bff47ba8e850f/Project.toml#L14.

@b-kloss we've decided to move the functionality in this repository to https://github.com/mtfishman/ITensorNetworks.jl, please move this PR over there if you plan to continue working on this.

Good question. Ultimately we plan to allow more general inputs to `tdvp` beyond MPS, for example tree tensor networks (#43), so it seems reasonable to allow `MPO` as well. A...

Just so I understand the issue fully, you are talking about implementing VUMPS in terms of a single MPO, not a sum of local MPOs, correct? Which kind of Index...

Oh I see, you are actually trying to write a general code for converting some sort of operator representation into a uniform MPO? Getting the indices consistent with the correct...

Amazing, thanks! My understanding is that the subspace expansion could be implemented by applying the 2-site effective Hamiltonian (the same one you would use in a 2-site VUMPS update), and...