issues: 520815068

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
520815068 MDU6SXNzdWU1MjA4MTUwNjg= 3509 NEP 18, physical units, uncertainties, and the scipp library? 12912489 closed 0     3 2019-11-11T08:45:29Z 2022-09-09T13:10:47Z 2022-09-09T13:10:47Z NONE      

This is an idea and meant as a discussion starter on an potential route to providing support for physical units and propagation of uncertainties for xarray.

Context

  1. NEP 18 (which, as far as I understand, was pushed by you guys, for similar purposes) provides means to combine such features with xarray using __array_function__, if the underlying array implementation supports it.

  2. I am working on scipp, which (based on a decision I may or may not regret in the future) is reimplementing a lot of features that xarray provides, plus some additional features. Two of these features are physical units and propagation of uncertainties.

  3. scipp.Variable is essentially equivalent to a numpy array with a unit, dimension labels, and an optional array of uncertainties. [*]

  4. scipp implements basic arithmetic operations (and some more) for scipp.Variable, including efficient propagation of uncertainties.

[] Caveat: scipp's current unit implementation is static an would probably need to be replaced for becoming useful for a wider audience.*

Idea and questions

Can we implement the __array_function__ protocol for scipp.Variable so it can be used with xarray? As far as I can tell this would simply be a lightweight wrapper.

  • Did I understand __array_function__ correctly?
  • Is there anything else I should be aware of?
  • Would anyone be interested in this?

This would amount to using the lower-level parts of scipp which is quite compact and can be extended to support more data types and more operations in a relatively simple manner (requiring recompilation, since it is written in C++).

 
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   completed 13221727 issue

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