Modif to basal stress calculation for computational efficiency (NEW one)

[JFLemieux73]

[Remove this and add a short summary line]:

• Developer(s): JF Lemieux

• Please suggest code Pull Request reviewers in the column at right.

• Are the code changes bit for bit, different at roundoff level, or more substantial?

It is BFB for the standard code (i.e. basal_stress = 'false').

It is not BFB when basal_stress = 'true' in the Northwern Hemipshere (it is .BFB in the Southern Hemisphere because there is no grounding with the bathymetry I used). I ran the gx3 config for one year for the latest code and this new code. The max. difference in thickness one year later (monthly mean) is 3 cm.

The new code for the basal stress is more computationally efficient (based on a suggestion from David Hebert, NRL). It is not BFB because I have changed the order of the operations.

I had a careful look at this and the differences are really due to small nonBFB differences.

I ran the testing script cice.t-test.py

INFO:main:Number of files: 1833
INFO:main:Two-Stage Test Passed
INFO:main:Quadratic Skill Test Passed for Northern Hemisphere
INFO:main:Quadratic Skill Test Failed for Southern Hemisphere
INFO:main:
INFO:main:Quality Control Test PASSED

It passes except in the Southerne Hemisphere...It is weird as it is BFB there.

• Is the documentation being updated with this PR? (Y/N) Y (done in previous PR)
  If not, does the documentation need to be updated separately at a later time? (Y/N)
  Note: "Documentation" includes information on the wiki and .rst files in doc/source/,
  which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.

• Other Relevant Details:

[JFLemieux73]

Ok it passes with the latest QC script (PR #145)

INFO:main:Number of files: 1833
INFO:main:Two-Stage Test Passed
INFO:main:Quadratic Skill Test Passed for Northern Hemisphere
INFO:main:Southern Hemisphere data is bit-for-bit
INFO:main:
INFO:main:Quality Control Test PASSED

[eclare108213]

@JFLemieux73 Thanks for testing both your code changes and the QC scripts!