UtilityFuncCRRA

[alanlujan91]

This PR creates an object oriented CRRA utility function to better organize namespaces and add formal structure to models.

• Tests for new functionality/models or Tests to reproduce the bug-fix in code.
• Updated documentation of features that add new functionality.
• Update CHANGELOG.md with major/minor changes.

[codecov-commenter]

Codecov Report

Base: 73.66% // Head: 73.38% // Decreases project coverage by -0.28% ⚠️

Coverage data is based on head (5dc1dc7) compared to base (ac76f68).
Patch coverage: 67.37% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1168      +/-   ##
==========================================
- Coverage   73.66%   73.38%   -0.29%     
==========================================
  Files          73       74       +1     
  Lines       12024    12150     +126     
==========================================
+ Hits         8858     8916      +58     
- Misses       3166     3234      +68     

Impacted Files	Coverage Δ
HARK/ConsumptionSaving/ConsRiskyAssetModel.py	41.03% <0.00%> (ø)
HARK/ConsumptionSaving/ConsPrefShockModel.py	79.68% <50.00%> (ø)
HARK/utilities.py	24.57% <50.00%> (-5.53%)	⬇️
HARK/rewards.py	54.44% <54.44%> (ø)
HARK/ConsumptionSaving/ConsMarkovModel.py	85.79% <54.54%> (-0.05%)	⬇️
HARK/ConsumptionSaving/ConsMedModel.py	73.99% <72.22%> (-0.06%)	⬇️
HARK/ConsumptionSaving/ConsAggShockModel.py	89.64% <80.00%> (ø)
HARK/ConsumptionSaving/ConsGenIncProcessModel.py	82.50% <84.61%> (+0.05%)	⬆️
HARK/ConsumptionSaving/ConsIndShockModel.py	86.40% <100.00%> (-0.10%)	⬇️
HARK/ConsumptionSaving/ConsLaborModel.py	82.97% <100.00%> (+0.07%)	⬆️
... and 7 more

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[sbenthall]

This looks like a good step forward to me!

[alanlujan91]

To do from @llorracc: look for standardized function representation (with derivatives and inverses) in other python libraries

[alanlujan91]

from scipy: https://docs.scipy.org/doc/scipy/reference/generated/scipy.interpolate.PPoly.html#scipy.interpolate.PPoly
from sympy: https://docs.sympy.org/latest/guides/custom-functions.html#differentiation

There does not seem to be a standard for mathematical functions.

[alanlujan91]

To do: Think of design for CRRA(CD) and/or CRRA(CES).

[sbenthall]

Looks like there's significant overlap between this PR and #1177

This looks like a simpler feature, and unless there's some good reason I'm not thinking of, it would be best to finish this one in its own PR.

[sbenthall]

Fix merge conflict please.

[alanlujan91]

The last discussion on this was that we need to settle on a standard before this is merged. Maybe I should close it for now.

[sbenthall]

My bad ...

[sbenthall]

@llorracc : advocates aligning this syntax with dolo's

[alanlujan91]

Would like to have all econ utility functions in HARK.utilities, but I think it's useful for econ UtilityFunction objects to inherit from MetricObject so they can be compared, ie what is the distance between utility functions? However, when I add from HARK.core import MetricObject into HARK.utilities I get a circular reference error because core.py inherits from utilities.py.

I would like to propose that the file utilities.py contains only classes/methods that pertain to econ utility functions, and everything else that is more of a programming utility to go into a file called tools.py or something like that. This would avoid the circular reference.

[alanlujan91]

TODO : labeled goods

[sbenthall]

@alanlujan91 See merge conflicts and test failures.

Punt the broader scope issues to #1035.
Lots of good stuff in this PR as is.

[alanlujan91]

now addresses #1188

[alanlujan91]

Changes in this PR:

• Move econ utilities to rewards.py.
• Rename parameter gam to rho in CRRAutility and derivatives.
• Fix ZeroDivisionError in all utility functions.
• Create cobb_douglas, cobb_douglas_p, cobb_douglas_pp, and cobb_douglas_pn functions.
• Create const_elast_subs and const_elast_subs_p functions.
• Implement abstract UtilityFunction class.
• Implement UtilityFuncCRRA class with derivative and inverse.
• Implement UtilityFuncCobbDouglas with derivative.
• Implement UtilityFuncCobbDouglasCRRA.
• Implement UtilityFuncConstElastSubs with derivative.
• Replace instances of CRRAutility with UtilityFuncCRRA throughout codebase.

[sbenthall]

I'll review this and merge if I don't see any issues.

[sbenthall]

Great work! Merging.