simplify nondimensionalisation of kinetics

[valentinsulzer]

Description

Simplifies non-dimensionalisation of the kinetics, which I think was making things overly complicated.

Previously, j0 was calculated as =

j0 = gamma * j0(...) / C_r

but

and we are currently scaling j0(...) as j0(...) = j0_dim(...) / j0_ref, so

j0 = gamma * j0_dim(...) / j0_ref / C_r = j0_dim(...) / j_scale

and if instead we scale j0(...) = j0_dim(...) / j_scale then

j0 = j0(...)

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Merging #2236 (6f56220) into develop (a1bc678) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #2236   +/-   ##
========================================
  Coverage    99.36%   99.36%           
========================================
  Files          357      357           
  Lines        19514    19514           
========================================
+ Hits         19390    19391    +1     
+ Misses         124      123    -1     

Impacted Files	Coverage Δ
...odels/full_battery_models/lithium_ion/basic_dfn.py	100.00% <100.00%> (ø)
..._battery_models/lithium_ion/basic_dfn_half_cell.py	99.01% <100.00%> (ø)
...odels/full_battery_models/lithium_ion/basic_spm.py	100.00% <100.00%> (ø)
...ybamm/models/submodels/interface/base_interface.py	100.00% <100.00%> (ø)
pybamm/parameters/lithium_ion_parameters.py	100.00% <100.00%> (ø)
pybamm/expression_tree/symbol.py	98.79% <0.00%> (+0.24%)	⬆️

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[valentinsulzer]

just sanity checking

[brosaplanella]

Looks good, thanks @tinosulzer!

[brosaplanella]

BTW, should we set a deprecation warning for the unused constants with the deprecated package?

[valentinsulzer]

BTW, should we set a deprecation warning for the unused constants with the deprecated package?

the parameters are still there, so where were you thinking of adding the warning?

Also I have no idea why that test is failing, and only on python 3.7

[brosaplanella]

Yes, not too fussed about the test.

I mean that, if the dimensionless numbers are not used, we might want to get rid of them eventually. If so, we can use deprecated to fail at a given release so we remove it.