Change objective normalization in weighted_sum decision method

[tsmbland]

Description

This changes the normalization in the weighted-sum decision method. Instead of normalizing objectives to [0,1] by subtracting the minimum and dividing by the maximum, we're now just dividing by the (absolute) maximum. See this comment for why I think this is a good idea.

There are probably other ways that this could be done, so happy to have a discussion about this.

Demonstrated below for the "LCOE" and "consumption" objectives

Single objectives:

Multiple objectives with weighted sum (before):

Multiple objectives with weighted sum (new):

With the new normalization method the behaviour looks much more in line with expectations (intermediate behaviour with 0.5/0.5 and equal to the single objective scenarios with 1/0 and 0/1)

I've also changed the tutorial models to use the "fuel_consumption_cost" objective instead of the EAC objective. I would have done this as a separate PR, but had to do it here as the original model didn't work with the changes I've made to the weighted sum method (it would jump between two solutions in the MCA and never converge). I think (hope) this is unrelated to the changes I've made to the weighted sum and just something that can happen sometimes. In any case, I think the "fuel_consumption_cost" is better for the tutorial as it has more contrast with the LCOE objective. See updated version here

Fixes #317
Fixes #337

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 (non-breaking, back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Key checklist

• All tests pass: $ python -m pytest
• The documentation builds and looks OK: $ python -m sphinx -b html docs docs/build

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

All modified and coverable lines are covered by tests ✅

Project coverage is 71.27%. Comparing base (0f1f518) to head (86e30d8).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #449      +/-   ##
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- Coverage    71.28%   71.27%   -0.01%     
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  Files           44       44              
  Lines         5885     5884       -1     
  Branches      1154     1154              
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- Hits          4195     4194       -1     
  Misses        1369     1369              
  Partials       321      321              

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[dalonsoa]

This looks really good! A very small change, a very big impact. I think the whole explanation of why this normalisation makes sense is solid, so happy with the changes.

[tsmbland]

This looks really good! A very small change, a very big impact. I think the whole explanation of why this normalisation makes sense is solid, so happy with the changes.

Great, thanks!