# Question about grouped parameter models

**URL:** <https://pybamm.discourse.group/t/question-about-grouped-parameter-models/446>\
**Category:** General\
**Created:** [29 January 2026 16:12 UTC](https://pybamm.discourse.group/t/question-about-grouped-parameter-models/446 "2026-01-29T16:12:29Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![oarcelus](https://avatars.discourse-cdn.com/v4/letter/o/46a35a/32.png) [@oarcelus](https://pybamm.discourse.group/u/oarcelus)\
**Post date:** [29 January 2026 16:12 UTC](https://pybamm.discourse.group/t/question-about-grouped-parameter-models/446/1 "2026-01-29T16:12:29Z")

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Hello, I am lookin at the grouped parameter model examples provided in PyBOB ([PyBOP/pybop/models/lithium\_ion/grouped\_spme.py at develop · pybop-team/PyBOP · GitHub](https://github.com/pybop-team/PyBOP/blob/develop/pybop/models/lithium_ion/grouped_spme.py)), for both SPM and SPMe models. I have a question about the definition of the evaluation of grouped parameters through the default parameters in `Chen2020` set. In this dataset electrolyte diffusivity and conductivity are functions of `c_e `and `T`. However in `GroupedSPMe` they are defined as `Parameter` instead of `FunctionParameter`, this is because the `default_parameter_values` method evaluates these parameters around `c_e0` and `T0` and gives a single `Scalar` value as a parameter.

I wonder how would you go around if you would like to group these parameters keeping the original concentration and temperature dependencies of Chen2020 parameter dataset. I guess defining `tau_e_` as a `FunctionParameter` is a step but not sure if the callable `De` can be assigned like that, given that the arguments of both functions will be different, one being `c_e/c_e_max` and the other `c_e`