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Hackmd copy from June 17 2023 sparse array followup meeting

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Author: dschult

content/summits/sparse/array-followup-2023-06-17.md

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+---
+title: "Summit Follow Up June 17"
+---
+
+# Friday June 17 2023, 14:00 to 15:00 UTC
+
+## Attendees
+
+- Dan
+- Erik
+- Isaac
+- CJ
+- Julien
+
+## Agenda
+
+- Sort out and attribute [what remains to be done](https://hackmd.io/1Q2832LDR_2Uv_-cV-wnYg#What-remains-to-be-done)
+- Roadmap/ plan for array-like sparse arrays
+  - Deprecation plan for matrices
+  - [Creation routines](https://github.com/scipy/scipy/issues/18592)
+  - Interop with other sparse matrix packages (isaac)
+- Blog post
+
+## Notes
+
+- Introduction, Erik works on libraries using sparse datastructures
+  - [Julien] Erik: here is [the worklog of the summit](https://hackmd.io/iEtdfbxfSbGwOAJTXmqyIQ)
+
+### What remains to be done
+
+- How do we work
+  - [Dan] Where does in-progress work go
+    - CJ's fork, make PRs onto branch there
+    - Using the view on the diff on GitHub might prevent the creation of spurious Draft PR
+  - Dense pretending to be sparse can be ephermeral, never needs to go to scipy
+  - Dan will make a branch for exploration that people can fork and make PRs to. Dan will try to keep it uptodate with the main branch too.
+- 1d sparse array support
+  Timeline? - Dan + CJ working on it - Targetting 1.12
+- nd sparse array support
+  - Julien, CJ: seems like low priority and this would be a huge maintainance cost SciPy for relatively rare use-cases
+  - CJ: Array api makes interop easier, we can lean on external packages for now
+- creation functions [scipy#18592](https://github.com/scipy/scipy/issues/18592)
+  - Want to get them out in a single release
+  - Is Ross going to implement these, or need to assign elsewhere?
+  - Current plan: `_array` methods, so we can apply this to the fast_matrix_market io at the same type
+  - Bundling in api changes (like tuples for shapes)
+- Deprecate `isspmatrix_` methods?
+  - Sounds like combination of classes + format attribute cover this
+  - (Julien) Deprecation plan: have suggested code to replace these things with
+  - Add a section in the documentation explaining the change of semantic and a migration plan for downstream libraries during the deprecation cycle.
+    - Make a roadmap for array api
+- scikit-learn
+  - When will scikit-learn be willing to support a compatible version of scipy?
+    - Julien:
+      - reasoning is based on some linux package manager not supporting latest numpy scipy
+      - Personally would like scikit-learn to follow SPEC 0
+      - See discussion for [1.3](https://github.com/scikit-learn/scikit-learn/issues/26438)
+      - [Dedicated RFC](https://github.com/scikit-learn/scikit-learn/issues/26418)
+      - Some part of scikit-learn's behavior depends on SciPy's version (e.g. see [this one](https://github.com/scikit-learn/scikit-learn/blob/784ba9ef9f65d5e4e33087dd7f5b87d65b605efc/sklearn/preprocessing/_polynomial.py#L61-L73)); we might potentialy rely on similar mechanism for the support of sparse arrays (e.g. reshaping outputs)
+      - scikit-learn uses nightly builds to test the developer version of SciPy and NumPy and failing tests are updated in [this issue](https://github.com/scikit-learn/scikit-learn/issues/26154). We can watch those for breakage in scikit-learn when we make changes in SciPy.
+- General speed ups
+  - "Fast path for canonical"
+    - TODO (Isaac)
+      - Figure out canonical for all the formats, probably normalize APIs
+      - Add keyword public argument for constructors
+
+## Broad plan for deprecation
+
+- Add support for sparse_arrays everywhere we can
+  - Creation functions: target 1.12
+  - 1d COO: target 1.12
+- Deprecate spmatrix-specific functions (where there's an easy replacement)
+  - Target: 1.12
+- Once everything works with sparse arrays, then deprecate spmatrix
+  - And the sparse array API is stable! (specifically, 1d support)
+  - Target: 1.13
+
+## Actionable items
+
+- [Julien] Add a section in the documentation explaining the change of semantic and a migration plan for downstream libraries during the deprecation cycle.
+- [Julien] Drop `isspmatrix_-` checks in scikit-learn and use `issparse` and `format`
+
+## Next meeting date and time
+
+- Every two weeks with the option to drop every other meeting (at least once a month)
+  > [name=Julien] +1. I proposed to meet every two week for 1h on the same timeslot