More simplifications

[valentinsulzer]

Description

More simplifications of the expression tree. Whenever there is a binary operator with a constant, the constant is moved to the left. This makes it easier to find constants.

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% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (6974c1c) compared to base (bc83ce7).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2424      +/-   ##
===========================================
- Coverage    99.72%   99.72%   -0.01%     
===========================================
  Files          258      258              
  Lines        19261    19184      -77     
===========================================
- Hits         19208    19131      -77     
  Misses          53       53              

Impacted Files	Coverage Δ
pybamm/expression_tree/averages.py	100.00% <100.00%> (ø)
pybamm/expression_tree/binary_operators.py	100.00% <100.00%> (ø)
...bamm/expression_tree/operations/evaluate_python.py	99.29% <100.00%> (-0.01%)	⬇️
pybamm/expression_tree/scalar.py	100.00% <100.00%> (ø)
pybamm/expression_tree/state_vector.py	100.00% <100.00%> (ø)
pybamm/expression_tree/symbol.py	100.00% <100.00%> (ø)
pybamm/models/submodels/interface/sei/base_sei.py	100.00% <100.00%> (ø)
pybamm/solvers/base_solver.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[rtimms]

thanks, looks good!

[valentinsulzer]

The benchmarks are slower for setup but faster for solve