allow custom initial state

[aabills]

Description

Allows for custom implementation of set_initial_state. Open to other ways of doing this.

Fixes # (issue)

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #)

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: nox -s pre-commit
• All tests pass: nox -s tests
• The documentation builds: nox -s doctests
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.78%. Comparing base (f1ceff2) to head (9cf223d).

Files with missing lines	Patch %	Lines
src/pybamm/parameters/parameter_values.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5215      +/-   ##
===========================================
- Coverage    98.79%   98.78%   -0.01%     
===========================================
  Files          320      320              
  Lines        27092    27099       +7     
===========================================
+ Hits         26766    26771       +5     
- Misses         326      328       +2     

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[valentinsulzer]

I don't really like putting it as a parameter because it's a different "type" of thing, it seems more natural to make it a method of a custom subclass of ParameterValues

[aabills]

I don't really like putting it as a parameter because it's a different "type" of thing, it seems more natural to make it a method of a custom subclass of ParameterValues

That's fine with me, I left it as that because that's where we keep "chemistry", which is used for this and only this. Shall I remove the "chemistry" parameter as well?

[valentinsulzer]

Yes let's remove chemistry as well On Mon, Sep 29, 2025 at 4:56 PM, Alec Bills ***@***.******@***.***>> wrote: [https://avatars.githubusercontent.com/u/48105066?s=20&v=4]aabills left a comment (pybamm-team/PyBaMM#5215)<#5215 (comment)> I don't really like putting it as a parameter because it's a different "type" of thing, it seems more natural to make it a method of a custom subclass of ParameterValues That's fine with me, I left it as that because that's where we keep "chemistry", which is used for this and only this. Shall I remove the "chemistry" parameter as well? — Reply to this email directly, view it on GitHub<#5215 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AE62MZM7TXIXAARYY7CMFOD3VGMFVAVCNFSM6AAAAACH2H556GVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTGNBZGAZDIMBUGQ>. You are receiving this because your review was requested.Message ID: ***@***.***>

[aabills]

Just pointing out that's a breaking change

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