Issue 710 atol klu

[Scottmar93]

Description

The bug was appearing because setting the atol vector is attached to the solver. If you then call the solver on a different model with a different number of states, it will break.

Fix: the atol vector is now attached to the model (via model.atol) and not the solver. If model.atol exists then the solver will use it otherwise it will use self.atol (the scalar value). Users can still set and change the scalar value for a solver and reuse that on different models but vector atols (which are model and dicretization specific) are attached to the model.

Fixes #710

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)
• 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

[valentinsulzer]

Looks great, thanks!

[codecov]

Codecov Report

Merging #721 into master will increase coverage by <.01%.
The diff coverage is 80.95%.

@@            Coverage Diff            @@
##           master    #721      +/-   ##
=========================================
+ Coverage    98.1%   98.1%   +<.01%     
=========================================
  Files         175     175              
  Lines        9190    9196       +6     
=========================================
+ Hits         9016    9022       +6     
  Misses        174     174

Impacted Files	Coverage Δ
pybamm/solvers/dae_solver.py	99.45% <ø> (ø)	⬆️
pybamm/solvers/scikits_dae_solver.py	97.72% <ø> (ø)	⬆️
pybamm/solvers/idaklu_solver.py	83.33% <80.95%> (+1.04%)	⬆️

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