Issue 688 add simulation class

[Scottmar93]

Description

Convenience class for interacting with the front-end of PyBaMM. I have set it up to try to be Jupyter notebook friendly in that things won't break if you try to build twice or solve without first building. It'll also automatically reset everything if you decide to change a spatial_method / parameter etc. Would be good to add some functionality on saving an loading later as well as allowing for experiment specific things to be set such as the current.

Fixes #688

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.

• New feature (non-breaking change which adds functionality)

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

[rtimms]

thanks @Scottmar93 look good! just a couple of comments

[codecov]

Codecov Report

Merging #693 into master will decrease coverage by 0.23%.
The diff coverage is 82.44%.

@@            Coverage Diff             @@
##           master     #693      +/-   ##
==========================================
- Coverage   98.52%   98.28%   -0.24%     
==========================================
  Files         175      176       +1     
  Lines        8861     8982     +121     
==========================================
+ Hits         8730     8828      +98     
- Misses        131      154      +23

Impacted Files	Coverage Δ
pybamm/parameters/parameter_values.py	99.51% <100%> (+0.02%)	⬆️
pybamm/discretisations/discretisation.py	99.71% <100%> (ø)	⬆️
pybamm/simulation.py	79.46% <79.46%> (ø)

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[valentinsulzer]

Really good idea making this so that jupyter notebooks don't break. I would just say that it might be cleaner to keep a copy of the original model, and then add options to parameter values to return a new model (i.e. not inplace). Discretisation already does this. Then the sim class could have self.model, self.parametrized_model, self.discretised_model. I don't feel super strongly about this though if you want to keep as is :)

Also, we should make discretisation of an already discretised model just return the same model, not break (different issue)

Otherwise, agree with Rob's comments.

[brosaplanella]

Just the comment about parameters, the rest looks good to me.

[TomTranter]

Looks good but I am not able to pickle the simulation object which is unfortunate due to a local object:

'''import pybamm
import pickle

model = pybamm.lithium_ion.SPM()
sim = pybamm.Simulation(model)
sim.solve()
sim.plot()

with open('test_save_sim', 'wb') as f:
pickle.dump(sim, f)
'''
I think it is to do with the solver object and possibly some recursive object referencing. We will have to discuss how to save and load simulations in future but as it stands this looks good and should be merged

[rtimms]

looks great thanks @Scottmar93 !