MPO construction and compression principles (or: how does OpSum work?)

[ryanlevy]

For construction, I would recommend checking out if you haven’t

• [0708.1221] Finite automata for caching in matrix product algorithms
• [0804.2509] Infinite size density matrix renormalization group, revisited

And this paper on MPO compression

• [1909.06341] Local Matrix Product Operators: Canonical Form, Compression, & Control Theory

I’ll have to let others comment on the exact compression techniques that are in ITensors