Matt Fishman

I didn't know about [`KrylovKit.realeigsolve`](https://jutho.github.io/KrylovKit.jl/stable/man/eig/#KrylovKit.realeigsolve), that's really cool! That's something I've wanted in multiple projects and wasn't even sure if it was possible/practical to do. @JoeyT1994 this is something we...

> I measured the impact of `eigsolve_eager` and it is small but noticeable. The following is with `eigensolve_krylovdim=10` and `eigensolve_maxiter=10` with an already well converged MPS (what I imagine the...

> > The difference should get larger as you make `eigsolve_krylovdim` larger. > > That's what I expect as well, but 10 with 10 iterations is already 33x larger than...

@corbett5 could you move this PR over to https://github.com/ITensor/ITensorMPS.jl? All of the MPS/MPO code is over there now.

I'll close this PR since it needs to be moved to the ITensorMPS.jl repository.

I assume I'll have to add more methods for `BlockInds`, but I wanted to see what were the minimal functions needed to get tests passing and also get feedback on...

That's the same as when you make a `BlockDiagonal` with `Diagonal` blocks: ```julia julia> D = BlockDiagonal([Diagonal([1, 2]), Diagonal([3, 4])]) 2×2-blocked 4×4 BlockMatrix{Int64, Diagonal{Diagonal{Int64, Vector{Int64}}, Vector{Diagonal{Int64, Vector{Int64}}}}, Tuple{BlockedOneTo{Int64, Vector{Int64}}, BlockedOneTo{Int64,...

Note that it works if I configure `Git.jl` to use my systems git installation as outlined here: https://github.com/JuliaVersionControl/Git.jl/issues/49#issuecomment-1810722774.

> I guess this would support blocks-within-blocks via `blockrange([blockrange(...), blockrange(...)])`? In principle, yeah, of course you would need a generalized `AbstractBlockedUnitRange` type to accommodate that, so maybe as a fallback...

This may require using [Git.jl](https://github.com/JuliaVersionControl/Git.jl), as discussed here: https://discourse.julialang.org/t/how-to-change-branch-name-using-libgit2/84353