Intent inout in shortwave_dEdd_set_snow

[dabail10]

This fixes a bug where the variables fs and hs should be intent inout in shortwave_dEdd_set_snow. This change is bfb in icepack except for hobart_nag_restart_col_1x1_alt03. This is with ktherm=1 and the topo poinds. All of the hobart_intel tests passed and were bfb. I'm not sure why this one case is not bfb.

• Developer(s): D. Bailey

• 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? NOT BFB

• To verify that this PR passes the initial QC tests, lease include the link to test results
  or paste in below the summary block from the bottom of the testing output.

• Does this PR create or have dependencies on CICE or any other models?

• Is the documentation being updated with this PR? (Y/N)
  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:

@eclare108213 REVISION TO THESE NOTES: As noted below, this merge is not BFB.

[apcraig]

A little worried about not bit-for-bit, but willing to approve. Did you do any bit-for-bit testing in CICE?

[dabail10]

Running the CICE base_suite again.

Dave

[dabail10]

So, I just compared back to some CICE baselines on cheyenne awhile ago. All of my tests are different with CICE master. So, maybe this is a compiler change on cheyenne? I guess I will go back and regenerate the baselines from CICE master again.

[dabail10]

Ok. So, 27 out of 32 compares failed in the CICE base_suite with this single change. The issue is the following in pseudo-code:

fs = c0
hs = c0

call set_snow(fs,hs)

...

later use fs/hs in a calculation

subroutine set_snow(fs,hs)

intent (in) fs,hs

hs = vsno / aice

if (hs >= hs_min) then
fs = c1
if (hs0 > puny) fs = min(hs/hs0,c1)
endif

So, when fs and hs are intent(in), this means the initialization earlier is ignored. In the subroutine "set_snow" hs is alway set, but fs might not be, i.e. when hs < hs_min. So, imagine a situation where the first time through hs = hs_min + eps. Then fs is set according to the min statement. However, the next time through maybe hs = hs_min - eps. Then fs is not reset to anything and it remembers it from the last call.

However, when fs and hs are intent(inout), they are always reset to zero before the call to "set_snow". I believe this explains the answer changes.

[apcraig]

OK, I assume it's right now and was incorrect before. It sounds like it changes answers. Thanks for running a test suite to check again.