More simplifications

[valentinsulzer]

Description

Still more simplifications

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

Base: 99.72% // Head: 99.72% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (c2c0f28) compared to base (d5547da).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head c2c0f28 differs from pull request most recent head 37b96d0. Consider uploading reports for the commit 37b96d0 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2443   +/-   ##
========================================
  Coverage    99.72%   99.72%           
========================================
  Files          258      258           
  Lines        19184    19211   +27     
========================================
+ Hits         19131    19158   +27     
  Misses          53       53           

Impacted Files	Coverage Δ
pybamm/discretisations/discretisation.py	99.79% <100.00%> (-0.01%)	⬇️
pybamm/expression_tree/averages.py	100.00% <100.00%> (ø)
pybamm/expression_tree/binary_operators.py	100.00% <100.00%> (ø)
pybamm/expression_tree/broadcasts.py	100.00% <100.00%> (ø)
pybamm/expression_tree/concatenations.py	100.00% <100.00%> (ø)
pybamm/expression_tree/symbol.py	100.00% <100.00%> (ø)
pybamm/expression_tree/unary_operators.py	100.00% <100.00%> (ø)
pybamm/meshes/meshes.py	98.07% <100.00%> (+0.29%)	⬆️
...lectrolyte_diffusion/base_electrolyte_diffusion.py	100.00% <100.00%> (ø)
.../submodels/electrolyte_diffusion/full_diffusion.py	100.00% <100.00%> (ø)
... and 3 more

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[brosaplanella]

Looks good, thanks!

[brosaplanella]

Suggested change

	- Added more rules for simplifying expressions, especially around Concatenations. Also, meshes constructed from multiple domains are now memoized ([#2443](https://github.com/pybamm-team/PyBaMM/pull/2443))
	- Added more rules for simplifying expressions, especially around Concatenations. Also, meshes constructed from multiple domains are now memorized ([#2443](https://github.com/pybamm-team/PyBaMM/pull/2443))

[valentinsulzer]

This refers to memoization https://en.wikipedia.org/wiki/Memoization, but I will change it to "cached"

[brosaplanella]

Oops, didn't know that, sorry! If it is a word, happy to keep it as it is.