fix experiment bugs

[valentinsulzer]

Description

Fix some bugs related to how an experiment is set up

Fixes #1700
Fixes #1702
Fixes #479

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 #1707 (32a49e7) into develop (58922b5) will increase coverage by 0.00%.
The diff coverage is 99.40%.

@@           Coverage Diff            @@
##           develop    #1707   +/-   ##
========================================
  Coverage    99.24%   99.24%           
========================================
  Files          344      345    +1     
  Lines        19037    19049   +12     
========================================
+ Hits         18894    18906   +12     
  Misses         143      143           

Impacted Files	Coverage Δ
...ybamm/models/submodels/electrode/base_electrode.py	100.00% <ø> (ø)
...trolyte_conductivity/leading_order_conductivity.py	100.00% <ø> (ø)
...dels/submodels/interface/kinetics/base_kinetics.py	100.00% <ø> (ø)
.../interface/lithium_plating/irreversible_plating.py	100.00% <ø> (ø)
...ls/interface/lithium_plating/reversible_plating.py	100.00% <ø> (ø)
.../submodels/particle_mechanics/crack_propagation.py	100.00% <ø> (ø)
pybamm/util.py	97.12% <ø> (ø)
...lyte_conductivity/base_electrolyte_conductivity.py	98.78% <91.66%> (-0.21%)	⬇️
...mm/expression_tree/operations/convert_to_casadi.py	100.00% <100.00%> (ø)
...bamm/expression_tree/operations/replace_symbols.py	100.00% <100.00%> (ø)
... and 25 more

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[rtimms]

nice, thanks @tinosulzer !

[rtimms]

revert to the default options?

[rtimms]

bye bye!

[brosaplanella]

Where was the issue?

[valentinsulzer]

I just made a new submodel for this. So now we have inverse butler-volmer for delta_phi_av and then another submodel for delta_phi. It's still a hack but now a "feature" instead of a "bug"

[valentinsulzer]

I am also thinking of combining the interface and conductivity submodels into one. It's the most confusing part of the submodels at the moment, because the way the interface and conductivity submodels interact is different based on whether you do forward or inverse kinetics. Combining them would mean more duplicate code but I think clearer