v0.13 Roadmap

[lkdvos]

MPSKit v0.13 - Derivatives update

As we are coming up to another set of breaking changes, this issue is meant to keep track of the remaining to-do's before we can release another version.

• Finish refactored derivatives Refactor derivatives and add JordanMPOTensor #270
• Add small benchmark suite to verify this
• Consistent use of below, operator, above argument order Consistent environments signature: below, operator, above argument order #268
• Change sector convention Change sector convention for excitations #271
• Update derivatives function names Refactor derivative names #276